About one million New Orleans people fled the low-lying southern US city on Sunday, as Hurricane Katrina starts whipping Louisiana.

"We are facing the storm that most of us have feared," said New Orleans Mayor Ray Nagin as he issued an unprecedented mandatory evacuation order for the city known as "The Big Easy."

"I do not want to create panic. But I do want the citizens to understand that this is very serious and it's of the highest nature," Nagin said.

The brunt of Katrina, which had 160-mph (266-kph) winds on Sunday evening, was expected to crash ashore around sunrise on Monday.

The storm had weakened slightly from the morning, when it boasted 175-mph (282-kph) winds, but it remained a savage Category 5 storm on the five-step Saffir-Simpson scale.

Mayor Ray Nagin warned the hurricane's storm surge of up to 28 feet (8.5 meters) could topple the levees protecting the city, which sits in a bowl-shaped area, and flood its historic French Quarter.

US crude oil prices have surged to a new record high of above US$70 US a barrel in opening trade on Monday amid concerns about supply shortages caused by the coming Katrina.

(Xinhua News Agency via agencies August 29, 2005)