"This certainly falls in the category of pretty much a worst case scenario."
The storm, which is expected to make landfall late on Friday or early on Saturday, is about 160km southeast of the city of Galveston and is on course to pass directly over Houston - the fourth-largest city in the US.
Ports were closed and the US Coast Guard said a ship with 22 people aboard was stranded without power 145 km off the US coast.
|Hurricane Ike comes in the midst of a heavy storm season [AFP]
Hundreds of thousands have fled Galveston and low-lying areas under mandatory evacuation orders.
Al Jazeera's Mike Kirsch in Texas said the storm was expected to affect 400km of the southern US coastline.
The authorities have urged those remaining to move before Ike's winds begin to make car travel dangerous.
In central Houston, around 80km inland from Galveston, businesses closed and windows were boarded up.
"Officials in Galveston say the main road [inland] has been cut off by water ... Officials are getting everyone inside, ready for the moment of truth," Kirsch said.
George Bush, the US president, said he was "deeply concerned" about the storm and for those in Texas, his home state.
The storm was also expected to cause further disruption to the oil industry, with refineries in Texas directly in Ike's path.
"Close to 20 per cent of the US refining capability could be lost for a long period of time," said Jim Rouiller, a meteorologist at Planalytics, a private weather forecaster.
Ike comes in the midst of a heavy storm season in the US and Caribbean and just 10 days after hurricane Gustav struck the US coast.
The hurricane has already battered the Caribbean, causing at least four deaths in Cuba, where over one million people were evacuated.