The massive round-the-clock project saw contractors drive piles into the gap, and huge twin-rotor Chinook helicopters dump hundreds of bags full of sand, cement, and bits of torn up roadways into the hole.

Hours before workers closed the breach late Sunday, gunmen opened fire on a team of contractors travelling to the site on the 17th Street canal, sparking a gunbattle with police.

"Work was completed on repairing the breach on the 17th Street Canal on Sunday night," Cleo Allen, spokeswoman for Louisiana's Department of Transportation and Development told AFP.

"They are now pumping water out of the canal and into the lake," Allen said, at the emergency operations center coordinating hurricane relief, 70 miles (120 kilometres) from New Orleans.

Engineers, who plan to blow holes in strategic points further down the levee to allow water to seep out, have calculated it will take between 36 and 80 days to drain the city.

That means it will be months before authorities can clean up the mess left by a toxic soup of floodwater, gasoline, sewage and other contaminents, which are posing a foul health hazard for the city.

Closing the 200 foot long (61 meter) breach marks a significant turning point for New Orleans, 80 percent of which was submerged by floods sending residents who had not evacuated scrambling for safety on their roofs.

Workers, coordinated by the Army Corps of Engineers had previously sealed the canal from Lake Pontchartrain on the northern edge of New Orleans, which as a bowl is below sea level and was hideously exposed to floods.

Military engineers were forced to build a temporary road to the site of the canal, after finding their route to the project blocked by debris and floodwaters.

The floods which engulfed New Orleans left an almost Biblical scene of destruction, compared by Homeland Security Secretary Michael Chertoff to an atomic bomb strike.

"This is probably the worst catastrophe, or set of catastrophes certainly that I'm aware of in the history of the country. It was a devastating hurricane followed by a devastating flood," Chertoff said on Saturday.

"That perfect storm combination of catastrophes exceeded the foresight of the planners and maybe anybody's foresight," he said as President George W. Bush's administration came under intense fire for its handling of the disaster.

But many observers say the set of events which shattered New Orleans had been predicted for years, in academic studies and probes by local newspapers.

Some local officials have also accused officials in Washington of cutting funds which could have been used to bolster flood defences to the vulnerable city.

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