Washington - As Hurricane Gustav took aim Sunday at New Orleans, reports said that US President George W Bush could cancel plans to speak to the Republican presidential convention due to start Monday.

Bush and Vice President Dick Cheney, who was also to speak Monday at the St Paul, Minnesota, gathering, plan to keep a watchful eye on the storm instead of attending the convention, media reports said, quoting a statement from White House spokesman Dana Perino. Both were slated to speak Monday night.

The presumptive Republican nominee, Senator John McCain, had raised the possibility of changing some plans for the Monday-to-Thursday event, saying it would be inappropriate to hold such a festive occasion while a major disaster loomed for US citizens.

A million people were fleeing their homes in New Orleans on Sunday as Gustav bore down on the city, hours after inflicting "considerable damage" in western Cuba.

New Orleans Mayor Ray Nagin bluntly told citizens: "You need to be scared. You need to be concerned, and you need to get your butts moving out of New Orleans right now. This is the storm of the century."

Gustav strengthened to a dangerous category 4 hurricane late on Saturday, on the 1-to-5 Saffir-Simpson Hurricane Scale. The storm was expected to make US landfall on Monday by noontime local time (1500 GMT).

In 2005, Hurricane Katrina wreaked devastation on New Orleans with a flood surge that left tens of thousands stranded for days without food and water while the federal government failed to act.

The catastrophe of delayed intervention was among the blackest marks dealt the Bush administration during its eight years in office.