The footage, obtained by the Associated Press, also shows Mr Bush being told of the risk to evacuees in the Superdome.

Speaking by video link from his Texan holiday ranch on 28 August, Mr Bush tells federal disaster officials: "We are fully prepared to help."

Critics say more could have been done sooner to evacuate the city.

Mr Bush does not ask any questions as the situation is outlined to him.

I don't think anybody anticipated the breach of the levees

George W Bush, speaking after the disaster

The BBC's Justin Webb reporting from Washington said the footage did the president no favours.

It shows plainly worried officials telling Mr Bush very clearly before the storm hit that it could breach New Orleans' flood barriers.

In the past, the president has said nobody anticipated a breach but the video shows Michael Brown, the top emergency response official who has since resigned, saying the storm would be "a bad one, a big one".

"We're going to need everything that we can possibly muster, not only in this state and in the region, but the nation, to respond to this event," Mr Brown says.

Earlier the Associated Press said Mr Bush had been warned of the levees being breached in the video.

But subsequently it issued a clarification which said that the president was warned about water overrunning the levees rather than breaking them.

The Army Corps of Engineers considers a breach a hole developing in a levee rather than an overrun.

'Very, very grave'

Another official, Max Mayfield of the National Hurricane Center, tells the final briefing that storm models predict minimal flooding inside New Orleans during the hurricane.

It surprises me that if there was that kind of awareness, why was the response so slow?

New Orleans Mayor Ray Nagin

His concern was borne out by events when levees collapsed, letting in the floodwater disastrously.

New Orleans Mayor Ray Nagin, shown the footage for the first time at a press conference, told Reuters he was "shocked" by what it revealed.

"It surprises me that if there was that kind of awareness, why was the response so slow?" he asked.

But Homeland Security spokesman Russ Knocke said most transcripts of discussions had already been made available to congressional investigators examining the response to Katrina.

"There's nothing new or insightful on these tapes," he said.

Mr Bush has accepted he shared some of the responsibility for the flawed response to Katrina and the White House has talked of the "fog of war" rendering decision-making difficult.

Michael Brown told AP this week that he did not "buy the 'fog of war' defence".

"It was a fog of bureaucracy," he said.