Washington - Thousands of residents along the Texas coast were evacuating on Thursday as Hurricane Ike took aim at the US mainland.

Ike, a category two storm on the five-level Saffir-Simpson scale, with 160 kilometre per hour winds could strengthen into a major category three hurricane before making landfall late Friday, the US National Hurricane Centre in Miami said.

Thursday afternoon the storm was about 645 kilometres east- southeast of Galveston, Texas and was moving toward the coast at 17 kilometres per hour.

Forecasters said Ike was "a very large tropical cyclone" and would bring high tides and strong winds before the storm itself reaches the coast. Hurricane force winds extended outward 185 kilometres from the storm's centre.

Officials in the Houston area had called for evacuations of low- lying areas and mandatory evacuations were underway in other coastal areas, including the popular beach resort of Galveston, the Houston Chronicle newspaper reported.

Texas Governor Rick Perry warned that water could reach the eaves of some houses in Galveston and told residents to leave.

"My message to Texans is, in the projected impact area, finish your preparations because this is a storm that can have extraordinary impact on them, on their personal belongings," the newspaper quoted him as saying. "It's on its way."

The storm could test the state's emergency plan that was revamped in the wake of Hurricane Rita in 2005, when evacuees clogged highways and drained petrol stations bringing the state to a standstill, the newspaper said. Broadcast images showed lines of cars filling the northbound highways.

The National Hurricane Centre said storm surge flooding could bring tides up to 6 metres above normal levels and dangerous waves. Ike could also dump from 13 to 25 centimetres of rain along the Texas and Louisiana coasts.

Perry had declared 88 counties disaster areas to free up funds to respond to the storm. Up to 7,500 members of the Texas National Guard were preparing for the landfall and the state had set aside thousands of buses to take evacuees inland.

US space agency NASA closed its Johnson Space Centre in Houston, moving operations to back-up facilities and flying aircraft to another site.