Reuters  – Hundreds of people fled areas near Texas rivers that overflowed their banks on Thursday as the state reeled from severe storms this week that killed at least 17 people, flooded cities and set a record for the wettest month.

The National Weather Service issued a flash flood watch stretching from south of San Antonio to Dallas, through Oklahoma, where severe weather this week killed an additional six people, and into Kansas. Thunderstorms pelted large parts of the affected region.

Teams worked overnight to rescue people affected by the flood waters. Officials said Travis County firefighters saved 21 people from a drifting houseboat while Johnson County emergency workers rescued 14 drivers and residents. No injuries were reported among them.

The city of Wharton, about 60 miles southwest of Houston, issued a voluntary evacuation notice for about 300 homes along the Colorado River, where water was expected to rise through Friday.

The Brazos River flooded about 30 miles west of Fort Worth and was expected to crest on Thursday evening. Hundreds left their homes on Wednesday as the waterway began breaching its banks, Parker County officials said.

State climatologist John Nielsen-Gammon said the average rainfall across the state was 7.54 inches in May, breaking the record of 6.66 inches set in June 2004, according to records that date to 1895.

"It has been ridiculous," Nielsen-Gammon said.

The body of a man was found on the banks of the Blanco River in San Marcos, authorities said on Thursday, bringing the number of fatalities to at least 17.

The man, who was discovered among flood debris, was not yet identified, according to Hays County officials.

The body of a boy was recovered on Wednesday near San Marcos, Hays County officials said. The boy was thought to have been swept away in Blanco River floods that ripped houses off their foundations.

The new storms could hinder rescue workers searching for those washed away along the river.

"We are not expecting another surge of the river, but it is going to shift debris piles," Kharley Smith, the county's emergency management coordinator, told a news conference.

President Barack Obama has pledged federal support and said the government had been working with local officials.

"They appear to have the assets they need at this stage to respond, but there's going to be a lot of rebuilding," Obama said in Miami on Thursday during a tour of the National Hurricane Center.

There was no damage estimate available for Texas, which has a $1.4 trillion-a-year economy and is the country's leading domestic source of energy.