Rescue teams have recovered more bodies in Texas, bringing the total death toll to 24 in the storm-lashed state.
The US president, Barack Obama, signed a disaster declaration late on Friday for areas in the state hammered by severe weather that also caused massive flooding and prompted evacuations throughout the week.
Storms that battered north Texas on Thursday and Friday added more runoff to swollen rivers and prompted hundreds of calls for help in Dallas, where some areas received up to seven inches (17.8 cm) of rain.
“Communities across the state of Texas have experienced devastating destruction, injury and, most tragically, loss of life due to the major and unceasing severe weather system that has been impacting our state for weeks,” said the Texas governor, Greg Abbott, who has declared 70 counties disaster areas.
The presidential declaration frees up federal funds to help rebuild. Residents and business owners who suffered damage were able to begin applying for aid this weekend, according to the statement from the White House.
No estimate has been given for the damage in Texas, which has a $1.4tn a year economy and is the biggest domestic energy provider.
Firefighters in the Dallas suburb of Mesquite recovered the body of a man who drowned in his truck after it was swept into a culvert. The bodies of two other men were found in the Houston area.
The body of 87-year-old Jack Alter, who was swept away when a boat trying to rescue him overturned, was found in the Houston Ship Channel. The search for a missing 51-year-old man was called off Friday after a body on a south-east Texas beach matched his description.
Near Dallas on Friday thousands of cars were trapped for about six hours on a suburban freeway blocked by floodwaters. The Red Cross distributed Girl Scout cookies and water to stranded motorists.
The National Weather Service issued a flash flood watch from central Texas into Missouri, with the additional rain tipping off a new round of flooding.
Dallas officials advised people to go home early and stay off the streets. “This would be a great night to stay home, watch a movie and cook some popcorn,” Dallas police deputy chief Scott Walton told a news conference.
The mayor of Wharton, about 60 miles (96.5km) south-west of Houston, issued a mandatory evacuation order for about 900 people living near the Colorado river, which began flooding into the city on Thursday and has been rising steadily since.
Hundreds of Texans were staying in shelters after the floods turned streets into rivers, ripped homes off their foundations and swept over thousands of vehicles.
The rushing water trapped people in cars and houses. One Dallas-area police officer had to be plucked to safety by a helicopter.
The rainfall for May across the state has already set a new record and more storms were forecast for Texas over the weekend.
The Brazos river, which began overflowing its banks on Wednesday in Parker county about 30 miles west of Fort Worth, is expected to see another surge due to recent rains.
“This situation will get worse before it gets better,” said George Teague, the Parker county emergency management co-ordinator.
