At least one million coastal residents have begun stocking up on emergency supplies and preparing to evacuate southern Texas, the heart of the US oil industry.
Mark Sloan, an emergency management co-ordinator in a Houston town, said he expected a "very large" storm to hit the area by the weekend.
"We have to be aware of its size as it grows over the next 24 to 48 hours and what impacts it will have on Friday, Saturday and Sunday," he said.
Texas is home to 26 refineries that account for a quarter of US refining capacity, and most are clustered along the Gulf Coast in such places as Houston, Port Arthur and Corpus Christi.
Refineries are built to withstand high winds but flooding and power outages can disrupt operations, shutting equipment for days or weeks.
An extended shutdown could lead to higher oil prices.
New Orleans, still scarred by Hurricane Katrina which killed 1,500 people and caused $80bn in damage on the US Gulf Coast in 2005, appeared to be out of danger.
Trail of destruction
Hurricane Ike has already left a trail of destruction across Cuba, damaging at least 27,000 homes in the east.
|Ike caused a lot of property damage across Cuba and killed five people [AFP]
State-run media showed a panorama of destruction across the island, still reeling from the more powerful Hurricane Gustav 10 days ago.
Ike struck eastern Cuba on Sunday with 195kph winds and torrential rains that destroyed buildings, wiped out the electricity grid, toppled trees, levelled crops including sugarcane fields, and turned rivers into roaring torrents.
After up to 40cm of rain fell on the island the downpour continued on Wednesday even as Ike moved away, causing widespread flooding and growing alarm among officials.
A total of 2.6 million people were evacuated before Ike, or about 22 per cent of the country's 11 million population.
Officials said five people were killed.
Before Cuba, Ike hit Britain's Turks and Caicos Islands and the southern Bahamas as a ferocious Category 4 hurricane.
Floods triggered by its torrential rains were blamed for at least 71 deaths in Haiti, where Tropical Storm Hanna killed 500 people last week.