Lesterville, Mo. ? The stone retaining wall around a huge mountaintop reservoir in the Ozarks collapsed before daybreak Wednesday, releasing a billion-gallon torrent of water that swept away at least two homes and several vehicles and critically injured three children, authorities said.

The V-shaped breach opened up just after 5 a.m. at a hydroelectric plant run by St. Louis-based utility AmerenUE, and within minutes the 50-acre reservoir had emptied itself out with terrifying effect, turning the surrounding area into a landscape of flattened trees and clay-covered grass.

“We’ll never see anything like it in our lifetime again,” paramedic Chris Hoover said.

The cause of the accident was under investigation by federal regulators and other authorities, but utility officials said there was no evidence of foul play. The reservoir sits near a seismic fault line, but no earthquake was detected.

AmerenUE’s chairman said rain was not believed to be a factor either. There had been little rain over the past several days.

Tow truck driver Kerry Buckley drags a cable out to a truck that was washed off a highway after a billion-gallon torrent of water was released from a reservoir after its retaining wall was breached Wednesday in Lestervile, Mo.

Trucker Greg Coleman was hauling a load of zinc when a wall of water emerged from the darkness and slammed into his truck near the Taum Sauk Lake Hydroelectric Plant.

“I had no idea where it was coming from – I travel this road every day,” Coleman said.

Coleman said he heard a man screaming for help. The man’s home had been washed away. Badly bruised, he was clinging to a cedar tree while his young children held onto other trees. Rescue workers arrived and rescued the family.

The three children – ages 7 months, 3 and 5 – were listed in critical condition at a hospital in St. Louis, 120 miles to the northeast. The two older children had breathing problems; the baby suffered from hypothermia, authorities said.

The names of the children were not immediately released, but Gov. Matt Blunt said Jerry Toops, superintendent of a state park near the reservoir, and his three children were injured when the water hit their home.

The reservoir, built in 1963, was dug out of the top of 1,590-foot Profit Mountain, with huge, sloping, 90-foot-high walls made of the stone removed from the peak. The reservoir was lined with concrete and asphalt. A plastic liner was added two years ago because of minor leaks, said Gary Rainwater, AmerenUE chairman and chief executive officer.

Normally, water released from the reservoir normally rushes down a 7,000-foot shaft and tunnel and spins the turbines to generate electricity. In Wednesday’s accident, water gushed through the breach and streamed down the side of the mountain and into a valley, eventually flowing back into the Black River, AmerenUE said.

Soon after the break, police and the National Weather Service urged the 150 residents of Lesterville, about 150 miles downstream in the sparsely populated area, to move to higher ground. But by midday, once the water had flowed back into the river, the danger had passed.