WAYNESVILLE, Mo. — The first sign of trouble came from a gurgling noise emanating from the sink, bathtub and toilet in Katie Knight's home. She looked out the window early Tuesday to see floodwaters already lapping at her back deck.

"I panicked," said Knight, a 31-year-old disabled Army veteran. "It's an eerie feeling when you see waters rising, because you are at the mercies of God's hands."

The sudden flood that swamped the south-central Missouri city of Waynesville killed a 4-year-old boy who was swept from a vehicle, and authorities were still searching the water Tuesday for a woman who is believed to be the mother of the boy, who was found just upstream from Knight's home.

The floodwaters left others clinging to tree branches in swiftly moving high water and damaged about 100 homes and businesses, authorities said.

"The quickness of the storm, the depth of it, the amount of water that was flowing freely, caused havoc," said Pulaski County chief sheriff's deputy John Groves.

Although some of the water receded within hours, other larger rivers continued to rise throughout Tuesday and a forecast for more rain in the region led to fears of additional flooding in the coming days. About 200 Waynesville homes in low-lying areas were being evacuated because of the forecast.

Missouri Gov. Jay Nixon declared a state of emergency, and the Missouri State Highway Patrol sent extra troopers and equipment to help emergency responders.

The flooding was triggered after several days of rain in the region culminated in a rare August downpour.

National Weather Service hydrologist Mark Fuchs said more than 7 inches of rain fell at Fort Leonard Wood, which is near Waynesville, from midnight to mid-Tuesday morning — but unofficial gauges nearby had nearly 9 inches of rain.

When Knight saw the rising waters from a nearby creek, she called friends and her landlord and then waded through thigh-high water to a neighbor's porch to wait out the flood. She watched as a man sitting atop an SUV and clutching a tree branch screamed for help for several hours before rescue workers could reach him.

At another site where people were stranded, a boat carrying rescue workers tipped over and additional crews had to be called in to rescue them, Crain said.

Crain said that local officials planned a mandatory evacuation in low-lying areas to guard against the potential for a resurgence of floodwaters.

Flo Vaughan, 77, said she was awakened in the middle of the night by rescue workers banging on her door, but did not immediately leave because she didn't know who was there. She watched as the floodwaters tore out her fence, washed away her shed and shifted her 350-gallon propane tank from its base. The smell of gas still hung in the air later Tuesday in the neighborhood, and water continued to bubble up from manholes and flow down the streets.

"I'm a lucky one — it didn't get my house," Vaughan said.

About a dozen propane tanks were seen floating through the floodwater. Many of the tanks leaked, and in some places, the gas was a foot or two deep above the floodwaters, a fire threat that kept rescue boats away until the gas cleared.

Fuchs said the Fort Leonard Wood area has seen nearly a foot of rain since August began. This month's weather patterns are unusual, as there's usually little rain and higher temperatures in August.

The downpours have caused dramatic rises in several rivers and creeks. The Gasconade River at Hazelgreen was at 3 feet on Saturday; it crested at 29.5 feet late Tuesday afternoon, but still was short of the record of 34.9 feet in 2008.

Roubidoux Creek, which cuts through Waynesville, had only about a foot of water before the rain. On Tuesday, it reached a record 21 feet.