The mayor of New Orleans has ordered a mandatory evacuation for most of the residents of his southern U.S. city, as Hurricane Katrina nears with winds of 250 kilometers per hour.

Sunday, the U.S. National Weather Service upgraded Katrina to a rare category 5 storm, the most intense on the Saffir-Simpson hurricane scale.

Forecasters expect Katrina to make landfall in the state of Louisiana sometime Monday, bringing heavy rains and a high storm surge along with the winds.

Officials are especially concerned about New Orleans, most of which sits below sea level and is vulnerable to flooding. Weather officials have warned a major loss of life is possible unless residents take precautions immediately.

At last report, the hurricane was located about 400 kilometers off the southern Louisiana coast, in the Gulf of Mexico.

President Bush has already declared a federal state of emergency for the state of Louisiana.

Some information for this report provided by AP.