The first details emerged Friday on the cause of China's largest reported oil spill, while environmentalists urged the government to do more to warn local residents of potential danger, saying children are playing still off nearby beaches.
Chinese authorities gave no update Friday on the size of the oil spill, which had spread over at least 165 square miles (430 square kilometers) of water after a pipeline at the busy northeastern port of Dalian exploded a week ago.
The disaster has caused China to take a hard look at its ports, some of the busiest in the world.
The explosion was caused when workers continued to inject desulfurizer into the pipeline after a tanker had finished unloading oil, according to a statement posted Friday on the website of the State Administration of Work Safety.
The statement said the explosion remains under investigation. The pipeline is owned by China National Petroleum Corp., Asia's biggest oil and gas producer by volume. State media have said oil operations at the Xingang port have resumed.
China's transport ministry ordered ports across the country to have emergency response plans and hold regular safety drills, the state-run Xinhua News Agency reported Friday.
The ministry will also establish a database of all ports that handle dangerous goods, the People's Daily newspaper reported.
Officials have warned of a "severe threat" to sea life and water quality as China's latest environmental crisis spread off the shores of Dalian, once named China's most livable city. One cleanup worker drowned this week, his body coated in crude.
Cleanup workers have reported using chopsticks and their bare hands to remove the gooey oil from the sea, while state media said 2,000 soldiers, 40 oil-skimming boats and hundreds of fishing boats were helping with the cleanup.
Environmental group Greenpeace, which has a team at the scene, urged the government to warn residents on nearby coastlines of the dangers.
"Greenpeace was ... surprised to see that the beaches have not been closed to visitors and lack any warning signs," Greenpeace China said in a statement Friday evening. "As a result, locals and visitors unaware of the extent of the oil spill were playing in the water with their kids, risking exposure to petroleum."
It said fishermen without equipment were doing most of the cleanup work at one of Dalian's most popular beaches, Jinshitan.
"They don't even have face masks, the most basic and necessary of precautions. They don't even know that they need to protect their skin from crude oil," said Zhong Yu, one of the Greenpeace workers.
"We strongly urge the government to send professional staff and safety equipment to work on the cleanup process," Zhong said in the group's statement.
The foreign affairs office for the city of Dalian did not immediately respond to questions Friday about the cleanup or warning signs on beaches.
State media has said no more oil is leaking into the sea, but the total amount of oil spilled is not yet clear.
China Central Television earlier reported an estimate of 1,500 tons of oil has spilled. That would amount roughly to 400,000 gallons (1,500,000 liters) -- as compared with 94 million to 184 million gallons in the BP oil spill off the U.S. coast.
Associated Press researcher Yu Bing contributed to this report.