Water poured through a breach at a hydroelectric plant's rural reservoir in southeast Missouri on Wednesday morning, washing away homes and vehicles, authorities said.

A family of five was rescued after the breach about 5:30 a.m. at AmerenUE's Taum Sauk Lake Hydroelectric Plant, the Reynolds County Sheriff's Department said.

One person had been feared missing, but was later accounted for, sheriff's dispatcher Ginger Bell told a cable news station.

Conditions along the Black River, where the plant is situated, were considered dangerous, the National Weather Service said.

The plant is in the Ozarks, about 120 miles southwest of St. Louis.

"The Lesterville area and areas south along the Black River are in extreme peril," said Missouri State Highway Patrol Sgt. Marty Elmore. "We need to make every effort to have folks get to higher ground."

National Weather Service meteorologist Joe Pedigo said rescue teams were searching for people believed to be trapped in cars, especially along Highway N near the reservoir. Pedigo said a house, a mobile home, several cars and a tractor-trailer were reported washed away.

Pedigo said rain was not a factor in the break. The region received only about one-tenth of an inch of rain overnight, he said.

Reynolds County has about 6,700 residents.

The plant was built in 1963. Officials at AmerenUE, a utility based in St. Louis, said the breach occurred at the northwest corner of the reservoir that holds back 1.5 billion gallons of water from the Black River. It wasn't clear why the breach occurred, but AmerenUE officials said there was no obvious equipment failure, nor was there evidence of foul play.

"A number of AmerenUE engineers and specialists are investigating the incident; clearly, public safety is our top concern," said plant superintendent Rick Cooper.

AmerenUE spokeswoman Susan Gallagher said it wasn't immediately clear how much water escaped. She said crews were hustling to the scene to try and fix the breach.

Gallagher said the plant has four chief features -- the upper reservoir atop Proffit Mountain, a 7,000-foot-long shaft and tunnel, a powerhouse with two reversible pump turbine units and a lower reservoir formed by a dam across the Black River's east fork. The breach occurred at the upper reservoir.

During times of peak demand for electricity, water -- released from the upper reservoir -- rushes down the shaft and through the tunnel. As it passes through the powerhouse, the water spins the turbines to generate electricity, then is retained in the lower reservoir.