NEW ORLEANS (AP) - An explosion jolted residents awake early today, illuminating the pre-dawn sky with red and orange flames over the city where corpses rotted along flooded sidewalks and bands of armed thugs thwarted fitful rescue efforts.

Congress was rushing through a $10.5 billion aid package, the Pentagon promised 1,400 National Guardsmen a day to stop the looting and President Bush planned to visit the region. But city officials were seething with anger about what they called a slow federal response following the devastation left by Hurricane Katrina.

''They don't have a clue what's going on down there,'' Mayor Ray Nagin told WWL-AM Thursday night.

''Excuse my French - everybody in America - but I am pissed.''

At 4:35 a.m. Friday, an explosion rocked a chemical storage facility near the Mississippi River east of the French Quarter, said Lt. Michael Francis of the Harbor Police. A series of smaller blasts followed and then acrid, black smoke that could be seen even in the dark. The vibrations were felt all the way downtown.

Francis did not have any other information about the explosions and did not know if there were any casualties. At least two police boats could be seen at the scene.

It was the opening strike in yet another day of sadly deteriorating conditions.

Thursday saw tens of thousands being evacuated by bus to Houston from the hot and stinking Superdome. Fistfights and fires erupted amid a seething sea of tense, suffering people who waited in a lines that stretched a half-mile to board yellow school buses. The looting continued.

Gov. Kathleen Blanco called the looters ''hoodlums'' and issued a warning to lawbreakers: Hundreds of National Guard troops hardened on the battlefield in Iraq have landed in New Orleans.

''They have M-16s and they're locked and loaded,'' she said. ''These troops know how to shoot and kill, and they are more than willing to do so, and I expect they will.''

At the Superdome, group of refugees broke through a line of heavily armed National Guardsmen in a scramble to get on to the buses.

Nearby, about 15,000 to 20,000 people who had taken shelter at New Orleans Convention Center grew ever more hostile after waiting for buses for days amid the filth and the dead.

Police Chief Eddie Compass said there was such a crush around a squad of 88 officers that they retreated when they went in to check out reports of assaults.

''We have individuals who are getting raped, we have individuals who are getting beaten,'' Compass said. ''Tourists are walking in that direction and they are getting preyed upon.''

By Thursday evening, 11 hours after the military began evacuating the Superdome, the arena held 10,000 more people than it did at dawn. Evacuees from across the city swelled the crowd to about 30,000 because they believed the arena was the best place to get a ride out of town.