Tropical Storm Harvey has hit eastern Texas and Louisiana, bringing the catastrophic downpours that paralysed the US energy hub of Houston, where record rainfall drove tens of thousands of people from their homes.
The storm that first came ashore on Friday near Corpus Christi, Texas, as the most powerful hurricane to hit Texas in more than 50 years has killed at least 17 people and forced 30,000 people to flee to emergency shelters.
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Damage has been estimated at tens of billions of dollars, making it one of the costliest US natural disasters.
Clear skies in Houston on Wednesday brought relief to the fourth-largest US city after five days of downpours, as Harvey headed northeast, drenching cities including Port Arthur, Texas, and Lake Charles, Louisiana.
Some Houston residents began to leave emergency shelters, apprehensive about discovering what remained of the flooded homes they had fled.
As Harvey churned out of the Houston area, it made landfall for a third time early on Wednesday, and was about 40km west of Lake Charles, Louisiana, at 7am local time with winds up to 75km/h. It was expected to bring an additional 7.5 to 15.2cm of rain to an area about 128km east of Houston as well as southwestern Louisiana, where some areas have already had more than 45cm of rain.
The Beaumont-Port Arthur area east of Houston received "an incredible amount of rain overnight", said David Roth, meteorologist at the US Weather Prediction Center.
Harvey is projected to weaken as it moves inland to the northeast, the National Hurricane Center said.
It may take days for Houston's floodwaters, which have spilled over dams and pushed levees to their limits, to recede, local officials said.
As of Wednesday morning, Texas officials said almost 49,000 homes had suffered flood damage, with more than 1000 destroyed. About 195,000 people have begun the process of seeking federal help, FEMA said.
Houston Mayor Sylvester Turner imposed a curfew from 12am to 5am amid reports of looting, armed robberies and people impersonating police officers.
Texas is investigating hundreds of complaints of price gouging involving loaves of bread offered for $US15 ($A19), fuel for $US100 a gallon and hotels raising room rates, the state's attorney general said on Wednesday.
Moody's Analytics is estimating the economic cost from Harvey for southeast Texas at $US51 billion to $US75 billion.
The storm has affected nearly one-fifth of US refining capacity, sparking concerns about petrol supply. The national average petrol price rose to $US2.404 a gallon, up six US cents from a week ago, with higher spikes in Texas.
The unprecedented flooding has left scores of neighbourhoods in chest-deep water and badly strained the dams and drainage systems that protect the low-lying Houston metropolitan area, which is home to more than six million people and has an economy about as large as Argentina's.
Among the confirmed fatalities in Houston was Police Sergeant Steve Perez, a 34-year veteran of the force who drowned while attempting to drive to work on Sunday.
In Beaumont, northeast of Houston, a woman clutching her baby daughter was swept away in raging flooding. The baby was saved but the mother died, Beaumont police said.
In all, 17 people have died, according to government officials and the Houston Chronicle. Four volunteer rescuers also went missing after their boat was swept in a fast-moving current, local media reported.