Residents of some rural southeastern Texas counties braced for more flooding Tuesday along a river that had reached a record-high crest just two years after it had run dry in places because of drought.

The U.S. National Weather Service said the Brazos River crested at 16 metres Tuesday in Fort Bend County, which is just southwest of Houston and home to many suburbs. That eclipsed the previous record by one metre and exceeded levels reached in 1994, when extensive flooding caused major damage. About 1,000 have been forced from their homes in the area.

During four days of torrential rain, six people died in floods along the Brazos, which runs from New Mexico to the Gulf of Mexico.

A Brazos River Authority map shows all 11 of the reservoirs fed by the Brazos at 95 to 100 per cent capacity.

Four of the six dead were recovered in Washington County, located between Austin and Houston, County Judge John Brieden said. Lake Somerville, one of the Brazos reservoirs, was "gushing uncontrollably" over the spillway, threatening people downriver, he said.

About 40 people were rescued from late Sunday to Monday from homes in a low-lying neighbourhood flooded with up to one metre of water in Simonton, a town in Fort Bend County with about 800 residents. Aerial photos taken Sunday showed large swaths of the county under water.

The county had set up a pumping system to divert the water from the neighbourhood, which sits on a flood plain. But the water levels overpowered the system, according to Beth Wolf, a county spokeswoman.

Wolf said any additional rain in southeast Texas would be a problem.

"The ditches are full, the river's high, there's nowhere else for that water to go," she said.

Further south in Rosenberg, about 150 households had been evacuated by Monday, and city officials were co-ordinating with the county's office of emergency management to have rescue boats in place, according to spokeswoman Jenny Pavlovich. In neighbouring Richmond, a voluntary evacuation order was in place.

In Central Texas, a woman died Monday night in Austin when she was trapped in rushing water while tubing down a creek, a death an official blamed at least in part on recent heavy rains.

A man whose body was recovered late Sunday from a retention pond in the Austin area near the Circuit of the Americas auto racing track appeared to be one of two people reported missing earlier, said Travis County sheriff's spokeswoman Lisa Block.

There have been reports of others missing in Travis County, and crews were to resume searching Tuesday, but Block said there's no confirmation yet of additional missing people.

Elsewhere, authorities continued searching for the body of an 11-year-old boy who fell into a creek in Wichita, Kansas, and is presumed dead. Relatives have identified the boy as Devon Dean Cooley, who disappeared Friday night.

Devon's family, in a statement Monday, thanked firefighters for their tireless efforts to find the boy. The family held a cookout Monday evening to feed the rescue crews, followed by a candlelight vigil.

Scott Overpeck, a National Weather Service meteorologist, said Tuesday that the Brazos will recede in the coming days but that its levels will remain high for up to three weeks, in part because water will need to be released from the swollen reservoirs upriver.

"There's so much water on the Brazos that it's going to take a long time to drain through the whole river and drain out into the Gulf of Mexico," Overpeck said.