Harvey deluges cities, displaces 1 million

Mica Rosenberg and Emily Flitter
AAP
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Following the devastation of storm Harvey rescuers are now searching block by block for survivors.

A week after Hurricane Harvey came ashore in Texas, no let-up in rescue efforts is expected on Friday as large pockets of land remain under water after one of the worst and most costly natural disasters to hit the US.

The storm has displaced over a million people, with 44 feared dead from flooding that paralysed Houston, swelled river levels to record highs and knocked out the drinking water supply in Beaumont, Texas, a city of about 120,000 people.

Arkema SA and public health officials warned of the risk of more explosions and fires at a chemical plant owned by the firm. On Thursday blasts rocked the facility, about 40 km east of Houston and zoned off inside a 2.4 km exclusion zone, after it was engulfed by floodwater.

With the presence of water-borne contaminants a growing concern, the National Weather Service issued flood watches from Arkansas into Ohio on Friday as the remnants of the storm made their way through the US heartland.

The Neches River, which flows into Beaumont and nearby Port Arthur, was forecast for a record crest from Friday well above flood levels. The flooding and loss of drinking water forced the evacuation of a hospital on Thursday.

"Beaumont is basically an island," Mayor Becky Adams told a news conference on Thursday.

The city, situated about 130 kms east of Houston and largely cut off by floods, was only able to receive one major supply of drinking water on Thursday and there were plans to set up water distribution centres on Friday.

Harvey roared ashore late last Friday as the most powerful hurricane to hit Texas in half a century. It was downgraded to a tropical depression as it headed inland on Thursday, dumping unprecedented quantities of rain and leaving devastation across more than 500 km in the southeast corner of the state.

Moody's Analytics estimated the economic cost from Harvey for southeastern Texas at $US51 billion to $US75 billion, ranking it among the costliest storms in US history. Much of the damage has been to the Houston, the US energy hub.

At least 44 people are dead or feared dead in six counties including and around Houston, officials say. Another 19 remain missing.

Some 779,000 Texans have been told to leave their homes and another 980,000 fled voluntarily amid dangers of new flooding from swollen rivers and reservoirs, according to Department of Homeland Security acting secretary Elaine Duke.

Tens of thousands are in crowded evacuation centres across the region.

As floods began to recede in Houston, firefighters began conducting a house-by-house search to rescue stranded survivors and recover bodies as some residents returned to their homes to assess the damage.