Texas Governor Greg Abbott has said that "the worst is not yet over" for the south-east of the US state, after devastating Tropical Storm Harvey.
He said rain continues to fall and flooding in certain areas may last another week.
More than 20 people are reported dead, and large parts of the city of Houston are under water.
The storm has now moved on to neighbouring Louisiana, where flash-flood warnings have been issued.
Governor Abbott said Texas has carried out more than 8,500 rescues, and more than 32,000 people remain in shelters throughout the state.
Another 10,000 members of the National Guard are said to be on their way, joining the 14,000 already deployed to tackle the disaster.
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The storm, which previously reached hurricane status, has dumped record rainfall in the region.
However, meteorologists say much drier weather is forecast for Texas in the days ahead.
Authorities and volunteers are still battling to rescue stranded people.
The sheriff's office in Harris County has confirmed a family of six - two great-grandparents and four children - drowned while trying to flee the floods in a van.
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