As Hurricane Rita advances towards the north-west across the Gulf of Mexico, the National Weather Service said that it packs maximum sustained winds of nearly 175 mph and stands as the third most powerful Atlantic storm ever seen.

The statement was made based on pressure readings taken by 'hurricane hunter' aircraft.

Rita, which has been called 'potentially catastrophic,' sped onwards with forecasters predicting landfall on the Texas shore late on Friday or early Saturday, somewhere between Corpus Christi and Galveston.

Galveston was destroyed by a hurricane in 1900 in what still ranks as the deadliest natural disaster in US history.

Houston Mayor Bill White has called for the voluntary evacuation of low-lying neighbourhoods in the city.

Texas Governor Rick Perry expanded the evacuation zone: "If you're on the coast between Beaumont and Corpus Christi, now's the time to leave," he told a news conference.

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