Tropical storm Harvey has made a second landfall in the US state of Louisiana as large parts of Texas remain under water following record rainfall that forced tens of thousands of people from their homes.

Since coming ashore on Friday, the heavy rains have reportedly claimed the lives of at least 25 people and sent more than 32,000 to shelters, turning neighbourhoods into lakes in Houston, the country's fourth largest city.

On Wednesday, Harvey went on to swamp a stretch of coast from Port Arthur, Texas, to Lake Charles in neighbouring Louisiana.

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"The worst is not yet over for southeast Texas as far as the rain is concerned," Governor Greg Abbott said, referring to the area that includes Beaumont and Port Arthur.

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He warned residents of the storm-hit areas to expect floodwaters to linger for up to a week.

National Guard troops have rescued more than 8,500 people since the storm began, Abbott said.

A top county official on Wednesday said Harvey has taken two lives in Orange County, Texas.

Orange County Judge Stephen Carlton would only say the two died on Monday night in the city of Orange and that the deaths were storm related, according to The Associated Press. He provided no other details.

The fatalities bring the number of confirmed deaths to 25.

'Worst fears realised'

Taking advantage of a lull in the rainfall, rescuers on Wednesday recovered the bodies of six family members from a van which was swept away by the floods over the weekend.

Manuel and Belia Saldivar and four of their great-grandchildren - ranging from six to 16 years in age - went missing on Sunday as they were attempting to escape rising waters.

"We have a total confirmed six dead here at the scene inside this van," Harris County Sheriff Ed Gonzalez told a press conference. "Our worst fears have been realised."

IN PICTURES: Harvey causes havoc in Texas

With hundreds of people still unaccounted for, there is little doubt the final toll will rise further although officials stress many may simply have no access to phones or power.

"A third of the city remains under water," Al Jazeera's Heidi Zhou-Castro, reporting from Houston, said.

"That is unprecedented and up until this point rescuers have really used every minute of their time trying to reach the backlog of desperate calls for help to get to those who life is in imminent danger," she added.

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"As the waters are starting to recede, the emergency workers are just starting to catch their breath knowing that there are thousands of square kilometres that need to be combed in the search for those missing."

Outside Houston, more than 50cm of rain had fallen overnight in the communities of Beaumont and Port Arthur in eastern Texas, officials said.

The floods shut the country's largest oil refinery in Port Arthur, in the latest hit to US energy infrastructure that has sent gasoline prices climbing.

READ MORE: Facing Hurricane Harvey

Some 14,000 members of the Texas National Guard have been deployed and the total number was expected to climb to 24,000 members, including from other states, using some 600 vehicles, 500 boats and 100 helicopters.

Some 32,000 people were in more than 230 shelters, and the Federal Emergency Management Agency (FEMA) was beginning to move families out of shelters and into transitional housing at hotels.

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The Toyota Center arena in central Houston was opened on Tuesday to house additional flood victims. Some 10,000 people were already staying the George R Brown Convention Center, double the building's capacity.

Some 210,000 households had already registered with FEMA for financial assistance and 37 million dollars had already been provided, officials said.

Moody's Analytics is estimating the economic cost from Harvey for southeast Texas at $51bn to $75bn, ranking it among the costliest storms in US history.

Houston Mayor Sylvester Turner urged the government to quickly approve funds for relief efforts and clear any regulatory hurdles to recovery.

"I'm hoping that people at the federal level, at the very top, will understand this was catastrophic," Turner said at a news conference on Wednesday.

"We just need the red tape to be cleared. All of us have to act with a degree of urgency."

Source: Al Jazeera and news agencies