President Bush was warned before Hurricane Katrina struck that the storm could breach levees, put lives at risk in the New Orleans Superdome and overwhelm rescuers, according to video footage of last-minute briefings.

But the President did not ask any questions during a video conference with emergency staff and hurricane experts the day before Katrina came ashore on August 29 last year and assured soon-to-be-battered state officials: "We are fully prepared."

More than 1,300 people died during the hurricane and the widespread flooding that followed. A further 2,000 people remain missing six months after the storm. The Bush Administration has been severely criticised for its slow and chaotic response to the disaster.

The footage, obtained by the Associated Press (AP) news agency, shows federal officials predicting "the big one", a potentially catastrophic disaster on America's Gulf Coast, but a general lack of awareness that they did not have the resources to mount a recovery effort.

The detailed briefing, in which America's senior hurricane expert tells his colleagues there is "a very grave concern" over flood defences surrounding New Orleans, appears to contradict Mr Bush's statement, made four days after the storm, that "I don't think anybody anticipated the breach of the levees".

Mr Bush is shown confident in a small, windowless room under his ranch in Crawford, Texas, while Michael Brown, the much-maligned head of the Federal Emergency Management Agency (Fema) who resigned days after Katrina made landfall, looks ahead to the storm.

"My gut tells me this is bad one and a big one," Mr Brown told the briefing. "Everyone within Fema is literally on call."

"This is, to put it mildly, the big one, I think."

Mr Brown also expressed specific concerns about the plan to make the New Orleans Superdome a place of refuge if the city was flooded: "You may or may not know the Superdome is about 12ft below sea level," he told his colleagues before saying he doubted the strength of the roof.

Presaging his comments with a "not to be kind of gross", Mr Brown then said he was concerned about the ability of federal medical and mortuary teams to "respond to a catastrophe within a catastrophe".

The New Orleans Superdome, left without electricity and water, provided shelter for around 40,000 survivors in the aftermath of Hurricane Katrina and became one of the dominant images of the flawed recovery effort.

Mr Brown's unease was underlined by Max Mayfield, the director of the US National Hurricane Centre, who compared the approaching Hurricane Katrina, still 19 hours from landfall, to Hurricane Andrew, which hit Florida in 1992, causing $20 billion of damage.

"Right now this is a Category 5 hurricane, very similar to Hurricane Andrew in the maximum intensity but there is a big, big difference," Mr Mayfield said. "This hurricane is much larger than it ever was."

Mr Mayfield told the meeting it was the "wisest thing to do" to expect Katrina to hit the Gulf Coast as a Category 5 storm. The New Orleans levees were built to withstand a Category 3 hurricane.

On the question of the levees, Mr Mayfield told the emergency planners that the current path of the storm was unlikely to cause major flooding in New Orleans, but he warned a minor change of course could be deadly.

"If that track were to deviate just a little bit to the west, it would -- it makes all the difference in the world," he said, before adding: "I don't think any model can tell you with any confidence right now whether the levees will be topped or not, but that's obviously a very grave concern."

Joining the briefing once it had started, Mr Bush did not ask any questions, according to AP, before reassuring officials in Mississippi, Alabama and Louisiana, that the federal Government was poised to help.

"I want to assure the folks at the state level that we are fully prepared to not only help you during the storm, but we will move in whatever resources and assets we have at our disposal after the storm to help you with the loss of property and we pray for no loss of life of course," he said

The White House dismissed the video, saying it showed only one briefing, and did not add anything to the account of the Government's preparations for the storm that has emerged since the disaster and during a congressional investigation, which reported last month. A second, Senate inquiry is expected deliver its report within weeks.

"I hope people don’t draw conclusions from the President getting a single briefing," said a spokesman. "He received multiple briefings from multiple officials, and he was completely engaged at all times."

But Mr Brown, who was savagely criticised for his lack of emergency management experience in the days after the storm, said he hoped the footage would help diminish the blame that he has suffered both from the American public and the Bush Administration.

"I hope the residents of New Orleans, in fact, I hope the American public sees that Michael Brown, prior to landfall, was doing everything humanly possible to make this bureaucracy work and respond to this disaster, he said.

Mr Brown's claim that he was hampered by a "fog of bureaucracy" appears justified at one point in the August 28 briefing, when he tells his staff to cut through red tape if they have to: "Go ahead and do it," he said. "I’ll figure out some way to justify it... Just let them yell at me."

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