Waves from Hurricane Ike lash Texas coast
Residents in one area of the Texas coastline have been warned they must evacuate before the arrival of Hurricane Ike or "face certain death".
The National Weather Service issued the grave warning to those living in low-lying areas around Galveston Bay.
More than a million people in Texas have been advised to leave their homes before Ike hits early Saturday morning.
The storm has already killed more than 70 people in the Caribbean, with Haiti and Cuba particularly badly hit.
At 1500 GMT Ike was about 195 miles (320km) south-east of Galveston, with winds above 100 mph (160km/h).
The US National Hurricane Center (NHC) said Ike could strengthen from a Category Two to a Category Three storm - a "major hurricane" - by the time it reaches the coast.
The effects of the storm will be felt along the coast before it makes landfall.
The hurricane's predicted path will take it through Galveston and on to the US's fourth largest city, Houston.
Forecasters warned that because of the size of the storm, the low-lying coastal areas could be hit by a 20ft (6m) high surge of water.
"All neighbourhoods and possibly entire coastal communities will be inundated during the period of the peak storm tide," the National Weather Service said in a statement.
"Persons not heeding evacuation orders in single family one- or two-storey homes will face certain death."
The warning was issued after it became apparent that some residents in the Galveston Bay area were resisting orders to evacuate.
"There's more people here than I thought," Alicia Cahill, a public information officer for Galveston was quoted by the AFP news agency as saying.
The Texas authorities have laid on more than 1,000 buses to facilitate the exodus.
In Galveston - scene of the country's deadliest hurricane which killed at least 6,000 people in 1900 - 75 buses are transporting residents to the state capital, Austin.
Weak and chronically ill hospital patients are being moved to San Antonio, about 190 miles from Houston.
Authorities have ordered residents in Houston to stay put, to avoid a repeat of 2005, when some 110 people in the city died during a chaotic evacuation in the face of Hurricane Rita.
Almost all energy production in the Gulf of Mexico has been shut down as a precaution, but the US Department of Energy said the storm was expected to miss most of the installations.
President George W Bush has declared a federal emergency in Texas, allowing funds to be freed to help the state deal with the storm.
Hurricane Ike killed four people, wrecked tens of thousands of buildings and destroyed crops when it slammed into Cuba.
The UN estimates the cost of the damage at $3bn-$4bn (£1.7bn-£2.26bn).
The island nation was already reeling from the impact of Hurricane Gustav, which destroyed about 100,000 homes when it hit the island at the end of August.
Ike earlier caused 66 deaths in Haiti and reportedly damaged 80% of the homes in the Turks and Caicos Islands.
Haiti, the poorest country in the Western hemisphere, has endured the onslaught of four tropical storms in a three-week period, causing more than 550 deaths.
The UN has appealed for more than $100m (£57m) in international aid to assist Haiti, where most people live on less than a dollar a day.
The US has pledged $10m (£5.7m) in aid to Haiti, where the UN estimates 800,000 people are in temporary shelters.
Washington also offered $100,000 (£57,000) in initial aid to Cuba, whose government has been subject to a US trade embargo for four decades.
Cuba turned the offer down, asking instead that the US sells it supplies on credit.
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