Sirens in the North Dakota city of Minot are sounding to warn that the Souris River has begun to overtop levees earlier than anticipated.
The warning came five hours ahead of a looming deadline for nearly 11,000 residents to evacuate their homes for a second time in a month.
Water from the Souris River, which loops down from Canada through north central North Dakota, has been bloated by heavy spring snowmelt and rain on both sides of the border.
The resulting deluge is expected to dwarf a historic flood of 1969, when the Souris reached 1,554.5 feet above sea level. The river is expected to hit nearly 1,563 feet this weekend -- eventually topping the historical record of 1,558 feet set in 1881.