“We had a long night and we had a difficult night,” Gov. Joe Manchin said.

Manchin said there was still a sliver of hope for survivors and rescuers carried with them four extra oxygen packs, just in case. But even before they went back underground, officials had started using words like “recovery” and “bodies” more frequently.

Monday’s explosion killed at least 25 miners and four others were missing. There have been no signs since the day of the explosion that the four missing miners survived but authorities and their families are hoping they somehow made it to one of two refuge chambers that are stocked with four days’ worth of oxygen, food and water.

The first refuge chamber was found empty and when rescue teams tried to get to the second chamber early Friday, that’s where they encountered signs of fire and smoke, and had to retreat before they could determine if any miners were inside. Kevin Stricklin, coal administrator from the Mine Safety & Health Administration, said authorities may have to rely on cameras to check out that second chamber.

Search teams had gotten frustratingly close a day earlier to answers for the families of the missing miners — just 500 feet from the emergency chambers where any survivors would be — then were ordered to retreat because of volatile gas.

With the air deemed slightly safer four days after the blast and nitrogen being pumped in from above ground to neutralize explosive methane gas, rescuers went back in just before 2 a.m., navigating rubble strewn with bodies, twisted railroad track, shattered concrete block walls and mounds of dust.

To get so close three times, only to have to rush back to the surface again without completing their mission, has been difficult for the crews.

“It’s very emotional for all the rescuers,” Stricklin said.

Families were also on edge, said Manchin, who briefed the relatives before the news conference.

“We had to walk in and explain to them that we had a situation that no one wanted, but a situation that had to be dealt with,” Manchin said.

Stricklin said rescuers reached a first refuge chamber, stocked with air, food and water, and found it unused. They were on their way to a second chamber when they had to withdraw.

“The thing that is unknown is exactly where this fire is at,” Stricklin said.

As the world awaited news from the rescue teams inside the mine, more details emerged about the mine’s extensive list of safety violations. Federal regulators issued evacuation orders for all or parts of the Upper Big Branch mine more than 60 times since the start of 2009, according to a report prepared for Democratic Sen. Robert Byrd of West Virginia

In 2007, the mine met all the criteria to be declared by the Mine Safety and Health Administration to have a pattern of violations. This would have allowed for stricter oversight by the federal agency, including the potential shutdown of the mine, but Massey was able to reduce the number of the most serious violations and avoid the declaration.

MSHA has appointed a team of investigators to look into what happened, and President Barack Obama said he has asked federal mine safety officials to report next week on what may have caused the blast. Officials have suggested a buildup of methane may have been to blame.

Massey Energy has been repeatedly cited and fined for problems with the system that vents methane and for allowing combustible dust to build up. CEO Don Blankenship has strongly defended the company’s record and disputed accusations from miners that he puts coal profits ahead of safety.

Of the 25 confirmed dead, 18 bodies remain inside. Seven bodies were removed earlier in the week. Two other miners survived, and one of them remains hospitalized.

After rescue teams left the mine because of dangerous levels of poisonous gas, they waited around all day Thursday for another chance to go back in. The third trip was expected to be quicker because they had found a short cut to the search area, and would be able to ride on ATVs instead of trudging on foot after the underground rail cars run out of track. They had also left behind a lot of their gear to pick up on the way. Rather than two or three hours, the most recent trip was expected to take half that time.

For days, crews have been drilling holes into the sides of the mine to ventilate lethal carbon monoxide and highly explosive hydrogen and methane gas. Officials preferred that method to reduce the toxic levels, but realized late Thursday that the nitrogen would be needed.

Regina Lilly was at Arvon’s Floral in Whitesville buying a black and yellow ribbon arrangement to hang on her front door in support of the miners. She said she has been in rooms where officials let families know what’s happening.

“They want answers; they’re not getting answers,” she said. “They want their family members brought out of that mine; they haven’t got that yet.”

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Associated Press Writers Allen G. Breed, Greg Bluestein, Tim Huber, Vicki Smith and John Raby and videojournalist Mark Carlson in West Virginia; Mitch Weiss and Mike Baker in North Carolina; Ray Henry in Atlanta; and Sam Hananel in Washington contributed to this report.

Rescuers had to wait to enter the mine until crews drilled holes deep into the earth to ventilate lethal carbon monoxide, highly explosive hydrogen, as well as methane gas, which has been blamed for the explosion. The air quality was deemed safe enough for four teams of eight members each to go on what officials were still calling a rescue mission.

Officials and townsfolk alike admitted they didn’t expect to find any of the four missing miners alive more than two days after the massive explosion. Poisonous gases have filled the underground tunnels since Monday afternoon’s blast

But officials were holding out hope that the miners had somehow survived the explosion by escaping into airtight chambers with enough food, water and air to survive for up to four days.

Seven bodies had been brought out Monday and authorities want to recover 18 bodies of the known dead from the mine owned by Massey Energy Co., which has been cited for numerous safety violations.

The federal Mine Safety and Health Administration has appointed a team of investigators to look into the blast, which officials said may have been caused by a buildup of methane.

Massey has been repeatedly cited for problems with the system that vents methane and for allowing combustible dust to build up, including two large fines assessed in January when federal inspectors found dirty air flowing into an escapeway where fresh air should be, and an emergency air system flowing in the wrong direction. Miners were so concerned about the conditions that several told their congressman they were afraid to go back into the mine.

Even on the day of the blast, MSHA cited the mine with two safety violations — one involving inadequate maps of escape routes, the other concerning an improper splice of electrical cable. However, Kevin Stricklin from MSHA said those violations had nothing to do with the blast.

Massey CEO Don Blankenship has strongly defended the company’s record and disputed accusations from miners that he puts coal profits ahead of safety.

Rescue team members planned to carry 30 pounds of gear including breathing devices to protect them from bad air.

The rescue teams needed to trek some five miles from the mine’s entrance to the area the men might be. Underground rail cars called mantrips would take them as far as possible, but the rest would be on foot. Manchin said they had gone as far as they could before wrecked rails meant they had to walk the remaining “couple of miles” to an area where they hoped to find the miners.

“Families are very hopeful and very prayerful … That today we can put a finality to this today,” Manchin said.

The effect of so many sudden deaths in the area’s small coal-reliant communities started showing with obituaries for the victims appearing in local newspapers. The first five funerals were scheduled for Friday and Saturday.

Miner William “Bob” Griffith’s family was preparing for the worst. Griffith went to work Monday and never came home, said his brother, James Griffith, who also works at the mine. William Griffith’s brother-in-law, Carl Acord, died in the explosion.

“In my honest opinion, if anyone else survives it, I will be surprised,” James Griffith said.

Doug Griffith, another of William Griffith’s brothers and also a miner, sat down with his family after getting a briefing on the rescue effort, said his wife, Cindi.

“He just said we really need to prepare for the worst,” she said. “They don’t feel like there’s any hope.”

The mine produced more than 1.2 million tons of coal last year and uses the lowest-cost underground mining method, making it more profitable. It produces metallurgical coal that is used to make steel and sells for up to $200 a ton — more than double the price for the type of coal used by power plants.

The confirmed death toll of 25 was the highest in a U.S. mine since 1984, when 27 people died in a fire at a mine in Orangeville, Utah. If the four missing bring the total to 29, it will be the worst U.S. coal mining disaster since a 1970 explosion killed 38 in Hyden, Ky.

The explosion and its aftermath have gripped communities that rely on the income the mines provide in the heart of coal country.

Anna West, 34, joined about 300 people, many wearing the reflective orange stripes of the miners they love, to walk silently through the small town of Whitesville in a candlelight vigil for both the dead and missing.

She was with her three young children, thinking of their father, Claude West Jr., who has been a miner for eight years, the last several at the Kanawha Eagle mine.

“It could have just as well been my husband,” she said. “My father was a miner, his father was a miner.

“I already told my son that I don’t want him to be a miner.”

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Associated Press Writers Alan Breed, Greg Bluestein, Vicki Smith, Tom Breen, Tim Huber and John Raby and videojournalist Mark Carlson in West Virginia; Mitch Weiss and Mike Baker in North Carolina; Ray Henry in Atlanta; and Sam Hananel in Washington contributed to this report.