The most powerful hurricane to hit Texas in more than 50 years has killed at least 17 and forced tens of thousands to leave their homes.

Tropical Storm Harvey made landfall again on August 30 near the Texas-Louisiana border, adding more rain after a record downpour that has caused catastrophic flooding and paralysed the city of Houston.

The storm that first came ashore on August 25 as the most powerful hurricane to hit Texas in more than 50 years has killed at least 17 people and forced tens of thousands to leave their deluged homes.

Damage has been estimated at tens of billions of dollars, making it one of the costliest U.S. natural disasters.

There is some relief in sight for Houston, the fourth most populous U.S. city, with forecasters saying five days of torrential rain may come to an end as the storm picks up speed and leaves the Gulf of Mexico region later in the day.

Harvey, which made landfall west of Cameron, Louisiana on August 30, was expected to produce an additional 7.5 to 15.24 cm of rain to an area about 130 km east of Houston as well as southwestern Louisiana, where some areas have already seen more than 43 cm of rain.

It is projected to weaken as it moves inland to the northeast, the National Hurricane Centre said. “We aren't going to be dealing with it for too much longer. It's going to pick up the pace and get out of here,” said Donald Jones, a meteorologist at the National Weather Service in Lake Charles, Louisiana.

But nearly a third of Harris County, home to Houston, was under water, an area 15 times the size of Manhattan, according to the Houston Chronicle newspaper. It may take days for all flood waters, which have spilled over dams and pushed levees to their limits, to recede, local officials said.

Evacuees are airlifted in a U.S. Coast Guard helicopter after flooding due to Hurricane Harvey inundated neighbourhoods in Houston, Texas. Interstate highway 45 is submerged from the effects of Hurricane Harvey. Forecasters said Harvey’s onslaught was just the beginning. The National Hurricane Centre (NHC) in Miami warned “catastrophic flooding” was likely to occur in the days ahead. Debris lies on the ground in Rockport, Texas. Tornadoes spawned by Harvey damaged more than 50 homes in Fort Bend County, struck a commercial centre near Katy and tore through Cypress, while parts of the Houston region were evacuated ahead of record river floods. People are rescued by airboat, in Dickinson, Texas on August 27, 2017. Emergency responders completed more than 1,000 high-water rescues during the night. “Travel across the area is severely hampered, if not impossible,” said an announcement from the Weather Service. Evacuees leave a U.S. Coast Guard helicopter after being rescued from flooding, in Houston, Texas. Harvey bombarded the stretch of the Texas Gulf Coast with home-ripping winds and torrential rains. More than 3,00,000 people were without power after utility poles were knocked to the ground. This image made from a video shows a view from U.S. Route 59 of flooding on West Bellfort Avenue in Houston, on Aug. 27, 2017. The remnants of Hurricane Harvey sent devastating floods pouring into Houston Sunday as rising water chased thousands of people to rooftops or higher ground. People are evacuated from flood waters from Hurricane Harvey in a collector's vintage military truck belonging to a volunteer in Dickinson, Texas on August 27, 2017. Texas Governor Greg Abbott said he would activate 1,800 members of the military to help with the state-wide clean-up while 1,000 people would conduct search-and-rescue operations. Residents pick through needed items at a make-shift aid station, in Rockport, Texas on Sunday. While thousands fled the expected devastating flooding and destruction, many residents stayed put in imperilled towns and stocked up on food, fuel and sandbags. A car is submerged on a freeway flooded by Tropical Storm Harvey on Aug. 27, 2017, near downtown Houston, Texas. Harvey continued to head back toward the Gulf of Mexico at a slow pace.

City officials were preparing to temporarily house some 19,000 people, with thousands more expected to flee. As of Tuesday morning, nearly 50,000 homes had suffered flood damage, Texas officials said, and the tally is certain to rise.

Houston Mayor Sylvester Turner announced curfew from 12 a.m. to 5 a.m. amid reports of looting, armed robberies and people impersonating police officers.

U.S. President Donald Trump visited Texas on August 29 to survey damage from the first major natural disaster to test his leadership in a crisis. The President said he was pleased with the response, but it was too soon for a victory lap.

“We won't say congratulations,” he said. “We don't want to do that...We'll congratulate each other when it's all finished.”

Moody's Analytics is estimating the economic cost from Harvey for southeast Texas at $51 billion to $75 billion.

The unprecedented flooding has left scores of neighbourhoods chest-deep in water and badly strained the dams and drainage systems that protect the low-lying Houston metropolitan area whose economy is about as large as Argentina's.

The National Weather Service has issued flood watches and warnings that stretch from the Houston area into Tennessee.

The Interstate 69 highway is covered by flood waters from Tropical Storm Harvey on August 29, 2017, in Humble, Texas. | Photo Credit: AP

Harvey has drawn comparisons with Hurricane Katrina, which devastated New Orleans 12 years ago, killing 1,800 people and causing an estimated $108 billion in damage.

Former President George W. Bush was widely criticised for his administration's handling of the response to that disaster, taking a heavy toll on public support of his administration, and Mr. Trump clearly was aiming to avoid a similar reaction.

Among the confirmed fatalities was Houston Police Sergeant Steve Perez, a 34-year veteran of the force who drowned while attempting to drive to work on August 27.

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.

Ruben Jordan, a retired high school football coach died when he was helping rescue people trapped in high water, the Clear Creek Independent School District said.

In all, 17 people have perished, according to government officials and the Houston Chronicle. Four volunteer rescuers also went missing after their boat was swept in fast moving current, local media reported.

Residents within 2.4 km of a chemical plant in Crosby were also ordered to evacuate on Tuesday afternoon, due to the growing risk of an explosion and subsequent leak.

U.S. Coast Guard air units and boats have rescued more than 4,000 people. Thousands of others have been taken to safety by police, rescue workers and citizen volunteers who brought their boats to help, local officials said.

The National Hurricane Centre on August 29 afternoon said a record 131.78 cm of rain had fallen in Texas due to Harvey, a record for any storm in the continental United States.

This breaks the previous record of 122 cm set during tropical storm Amelia in 1978 in Medina, Texas, the NHC said. Medina is west of San Antonio. The island of Kauai was hit with 132 cm of rain from tropical cyclone Hiki in 1950, before Hawaii became a U.S. State.