|Hurricane Harvey filmed from space station|
Experts are warning the hurricane is "life-threatening" and poses a "grave risk" - prompting all seven coastal counties in Texas to order mandatory evacuations from low-lying areas.
Some supermarket aisles have been stripped bare as people stockpile food.
Harvey is currently a category-two hurricane (extremely dangerous winds will cause extensive damage) but is expected to whip up into a category three (devastating damage will occur) by the time it hits land late Friday or early on Saturday.
The eye of #Harvey is now visible on the Brownsville Radar. NHC will begin issuing hourly position updates at 11:00pm CDT.pic.twitter.com/OOFQr7SFoC— NHC Atlantic Ops (@NHC_Atlantic)August 25, 2017Harvey is predicted to first hit a 30-mile stretch of coastline about 70 miles northeast of Corpus Christi - where a children's hospital has airlifted 10 critically ill babies inland to Fort Worth.
"We're forecasting continuing intensification right up until landfall," said Dennis Feltgen from the National Hurricane Center - which is providing hourly Twitter updates on Harvey's progress .
"FOR ANYONE WHO HAS NOT ALREADY EVACUATED, PLEASE HURRY TO DO SO," the city of Portland, Texas, said on its website.
Up to 35 inches of rain is possible over southeast Texas over the coming days. Pic: NHC
America's fourth-biggest city, Houston, is also braced for impact as the hurricane is expecting to stall when it hits land and dump large amounts of rain over a number of days.
Authorities there have warned of 20 inches of rainfall and "dangerous flash flooding", and a total of 30 Texas counties are on disaster alert.
Sky News weather presenter Nazaneen Ghaffar said Harvey was set to "stall and meander for several days, leading to a devastating flood threat".
"There could be as much as 35 inches of rainfall from Harvey over the next few days," she added.
"Sustained winds of at least 111mph will likely cause destructive damage to buildings and transport lines and lead to large waves along the coastline."
Some supermarket aisles have been stripped bare as people stockpile food
The region's lucrative oil-refining business - known as "refinery row" - is also braced.
One drilling rig in the Gulf of Mexico has pulled out its staff, and 39 manned oil and natural gas platforms have been cleared, according to the Bureau of Safety and Environmental Enforcement.
|The last category three hurricane was Wilma, which hit Florida in 2005|
Lousiana, which was ravaged by Hurricane Katrina in 2005, has also put out an emergency declaration for the entire state.
The last category three hurricane was Wilma, which hit Florida in 2005
Hundreds of boats are standing by for potential rescues and half a million sandbags have been given out.
"This is going to play out over the next week or so," said governor John Bel Edwards, "which makes it particularly dangerous... because the longer it sits in one place the more rain that it will drop."
The last category-three hurricane to hit America was Hurricane Wilma, which hit Florida in 2005, and the last significant hurricane in Texas was Ike in 2008, which inflicted $22bn of damage.