There was no word on the cause of the blasts, which added a new dimension of panic to the historic city where thousands were still trapped amid foetid waters, rotting corpses and roving bands of gunmen and looters.

US television reported columns of smoke billowing from the southwestern section of New Orleans near the Mississippi River. CNN said authorities were trying to get hazardous material teams to the largely inaccessible area.

New Orleans was already on edge as Iraq-tested troops with shoot-to-kill orders moved in to stem growing anarchy that set in after Katrina pounded the US Gulf Coast on Monday, leaving thousands feared dead.

Bush was to tour three battered southern states Friday amid increasingly harsh criticism of his administration's handling of one of the worst natural disasters in US history.

Survivors and local officials complained bitterly the government was slow to speed troops and relief supplies to the New Orleans area, where up to 300,000 people were still feared trapped.

"This is a national disgrace," said Terry Ebbert, the head of New Orleans' emergency operations. "We can send massive amounts of aid to tsunami victims (in Asia), but we can't bail out the city of New Orleans."

US newspapers slammed Washington for its sluggish response, asking why it was so unprepared for such a long predicted tragedy. New Orleans Mayor Ray Nagin dropped all political niceties and said he was "pissed."

"Don't tell me 40,000 troops are coming down here," Nagin yelled into his telephone during a local radio call-in show. "They're not here. People are dying here."

Bush, accused of being slow to cut sort his holiday to deal with the crisis, was to make an aerial tour of hurricane-ravaged Louisiana, Mississippi and Alabama, the White House said.

The president, who has sworn a policy of "zero tolerance" for armed gangs and other hurricane profiteers, was also to make a statement on hurricane recovery efforts at Louis Armstrong New Orleans International Airport.

While Bush was to take to the air, officials moved to bolster security on the ground in New Orleans, throwing some 300 battle-hardened members of the Arkansas National Guard into the volatile situation

Louisiana Governor Kathleen Blanco said the guardsmen had been authorized to open fire on "hoodlums" profiting from the destruction.