The view from space indicates that the oil may be leaking at a rate of 25,000 barrels a day, dwarfing the figure of 5,000 barrels that US officials and the British oil giant BP have used in recent days.

A Northern Gannet bird, which is covered in oil from a massive spill in the Gulf of Mexico, pokes its head out from under a towel as members of Tri-State Bird Rescue and Research and the International Bird Research Center prepare to hydrate it in Fort Jackson, La., Saturday, May 1, 2010. (AP Photo/Patrick Semansky) That would mean that some nine million gallons may already have escaped from the underwater well following the April 20 explosion that killed 11 rig workers. It suggests the disaster will almost certainly prove greater than the Exxon Valdez tanker spill off Alaska in 1989, which released 11 million gallons and was the worst previous spill at sea.

President Barack Obama will visit the region on Sunday morning, aides have announced. The trip comes amid mounting criticism that the White House has been slow to react to the crisis.

His predecessor, George W Bush, faced similar anger over the federal government's handling of Hurricane Katrina in 2005. But the government has emphasised that responsibility for the clean-up rests with BP, which leased the rig and initially played down the scale of the leak.

As the administration steps up its operations, the Pentagon will spray the slick with chemical dispersants from military C-130 planes, although environmental groups warned that these could also seriously damage the eco-system.

Menwhile Eric Holder, the country's attorney general, is dispatching a team of lawyers to New Orleans to assess whether any laws have been broken. BP, which leased the rig and owned the oil rights, had downplayed the possible danger of any spill - predicting "no significant adverse impact" - when it submitted its exploration plan last year.

The scale of the looming catastrophe was still unclear yesterday as strong winds hampered an emergency operation to mop up the 2,200 sq mile slick being blown towards the coast of five US states.

Even BP has acknowledged that the 5,000-barrels-a-day figure for the leak - already a five-fold increase on the 1,000 barrels that it initially gave - is only a "guesstimate". The Coastguard has also said that that leak rate could turn out to be much greater than 5,000 barrels.

The implications of the higher figures for the fishing waters, wildlife and beaches of the Gulf - and the residents whose livelihoods depend upon them - are potentially devastating.

John Amos, director of SkyTruth, a satellite data monitoring outfit that supplies analysis to environmental groups, told The Sunday Telegraph that the images and information made public by BP indicated that the slick was made up of at least six million gallons of oil.

"That is a conservative estimate and it would mean that oil is leaking at a rate of 20,000 barrels a day," he said. "That's a real eye-opener. And I believe the true figure is significantly higher."

Ian MacDonald, a Florida professor of oceanography who tracks maritime oil seepage, estimated that more than nine million gallons may already have escaped into the sea on the basis of higher industry estimates of the rate of leakage. BP engineers have been desperately and unsuccessfully trying to use unmanned submarines to initiate a failed switch-off device on the well about a mile beneath the surface of the water.

In the absence of such a quick-fix solution, the company is pursuing two other remedies to stop the leak, but both will take weeks or months.

In the medium-term, the company is hoping to cover the leaks with 100-ton steel domes that would capture the escaping oil and funnel it back to a ship at the surface through pipes. The technology has been deployed for leaks at much shallower depths but has never been used for a deep-sea spill.

It has also dispatched a drill ship to the area to begin digging a relief well that would intercept the oil from the existing pipes at about 18,000 feet below the surface. This will allow the company to close off the leaking well, but the process will take at least three months and possibly much longer.

At the same time, investigations have been launched into the two crucial failures - why the rig exploded and then why the automatic switch-off device did not then activate. Oil industry analysts believe the explosion was caused by a "blow-back" when a pressure surge thrust natural gas up to the rig platform. One area under focus is a recently-completed cementing operation by the company Haliburton, which was intended to prevent oil and gas from escaping by filling gaps between the outside of pipes and the inside of the hole drilled into the ocean floor into which they fitted.

According to a 2007 US government report, cementing was a factor in 18 of 39 well blow-outs in the Gulf of Mexico over a 14-year period. And investigators have also been told that cementing was a likely cause of a major 10-week blow-out in the Timor Sea off Australia last year.

Haliburton has declined to comment while the cause of the accident is being investigated and lawsuits are pending.

The second disastrous failure occurred when the rig's "blowout preventer" - equipment that should have automatically blocked the well when the explosion occurred - failed to work. It has since emerged that the device did not have a remote-control shut-off mechanism - these are commonly required in most offshore oil producing nations, but not the US.

Fifty miles away, on the Louisiana coastline, communities that rely on the sea for their existence are now braced for the worst. Oyster beds could take 20 years to recover and world shrimp supplies will plummet as the Gulf waters are the largest source of the seafood.

There is widespread anger, not just at BP but also the federal government for what is perceived as a hopelessly tardy response. Locals have expressed disbelief that the deployment of booms - special floating barriers - to protect the coast only began nine days after the explosion.

In its initial statements, BP indicated that could handle the leak, but in recent days has appealed for urgent help from the government and other oil industry companies.

Mr Obama dispatched Cabinet ministers and top officials to the disaster zone on Friday. But there was resentment locally that he had not visited the region and he was last night [SAT] scheduled to deliver a humourous speech at the black-tie celebrity-studded White House Correspondents' Dinner in a Washington ballroom.

The announcement yesterday morning that he would make a trip to Louisiana today came as conservative critics called the oil spill "Obama's Katrina".

In New Orleans, Jeff Crouere, host of the "Ringside Politics" radio show, said that Mr Obama's approach to the crisis was being compared - unfavourably - to President Bush's handling of the fall-out from the hurricane.

"Five years on from Katrina, we feel another president has been ignoring us," he told The Sunday Telegraph.

"Another disaster in the Gulf of Mexico is heading for the shorelines of Louisiana. Once again, the federal government has bungled the response. In contrast to President Bush, who waited four days after Katrina to send federal help to New Orleans, President Obama has waited nine days to act after the horrific oil disaster in the Gulf.

"It should have been a top priority for the Obama administration in the minutes after the disaster, not waiting over almost ten full days to take serious action.

We are finally seeing the federal cavalry descending on the impact zone with booms, boats and personnel, but it is way too late. It would have been much easier to accomplish containment goals one week ago."

Another political embarrassment for Mr Obama is that he had only recently announced White House approval for a controversial expansion of offshore oil exploration.

The policy has been enthusiastically pushed by Republicans such as former vice-presidential candidate Sarah Palin - who litters speeches with the phrase "drill, baby drill" - and has also been backed by a majority of Americans since fuel prices soared.

But environmental groups and many members of the president's Democratic party are fiercely opposed to new drilling off America's coastline. And the White House said last week that no new licences would be granted while the cause of the current disaster is investigated.

Several lawsuits have been filed against BP, Transocean, the owner of the Deepwater Horizon rig, and other oil industry companies involved in the operation, on behalf of residents and businesses as well as survivors and relatives of those killed in the April 20 explosion.

But such legal matters were far from the minds of the hundreds of mourners who attended Friday's memorial service for Wyatt Kempt in the small rural Louisiana town of Jonesville Mr Kemp, 27, who was married to his teenage sweetheart and had two young daughters, worked on Deepwater Horizon for three years, following his own father into the dangerous world of the offshore oil fields.

"Wyatt liked the work and the money was good," said his grandmother, Carolyn Kemp. "There aren't many options for paying the bills round here." Indeed, Mr Kemp's brother Sandon will return to another rig after coming home to attend the service.

No bodies have been recovered from the waters. But a survivor told Mrs Kemp that there was no chance that her grandson escaped the series of blasts that ripped through the pumphouse where he was last seen.

When the rig exploded, he was just 75 minutes away from the end of his three-week stint at sea. Only the helicopter ride back to land should have awaited him.