Workers began Saturday directing underwater robots to replace the cap on a gushing well in the Gulf of Mexico, in a bid to finally contain the devastating oil flow.

Live video feed of the spill site showed remotely-controlled submarines maneuvering the cap system in order to remove the old containment cap and place a tighter one.

If all works as planned, the new cap combined with a series of tankers that on the surface could contain all the oil now soiling the Gulf's fragile coastlines as early as Monday.

But the new system, expected to take four to seven days to be operational, is only a temporary solution before relief wells are completed that could stop the flow completely -- and comes after repeated failures and setbacks for BP as it wrangles with the worstenvironmental disaster in US history.

Once the old cap is removed, oil will flow unabated into the Gulf waters for some 48 hours, and the new system's success is anything but guaranteed.

"This new sealing cap has not been deployed at these depths or under these conditions, and there can be no assurance that the sealing cap will be successfully installed or installed within the anticipated timeframe," BP warned in a statement.

BP senior vice president Kent Wells said other options remained at the ready, including a new "top hat" containment system, if necessary.

"We always have backups for our backups," he told reporters, noting that workers were also ramping up skimming activity to collect as much oil as spill site during recapping period.

Engineers nearly a mile (1,600 meters) above on the surface were manipulating the undersea robots, rushing to take advantage of about a week of expected favorable weather conditions in the spill area for the new operation.

The existing cap, which sucks up to 25,000 barrels (one million gallons) of oil a day, was installed over a month ago but it allowed some of the hydrocarbons to escape because it was loosely fitted over a jagged cut of the well pipe.

BP is also working to connect the Helix Producer containment ship to another portion of the blown-out well. The ship should be up and running by Sunday, officials said.

Government estimates for the disastrous spill unleashed when the BP-leased Deepwater Horizon rig sank nearly three months ago, range between 35,000 to 60,000 barrels of oil (1.5 million to 2.5 million gallons) spewing into Gulf waters each day, based on interpretation of a live video feed of the leak.

The new cap and containment ship will raise containment capacity to 60,000 to 80,000 barrels (2.5 million to 3.4 million gallons) a day -- in effect halting spill that has imperiled wildlife and people's livelihoods across the Gulf Coast, according to officials.

An estimated 2.9 to 4.9 million barrels of oil have gushed into the Gulf waters since the spill began, and on day 82 of the spill, only 755,900 barrels have been recovered.

The government's pointman on the spill, Coast Guard Admiral Thad Allen, said on Friday he had approved the latest plans because they will provide for "far greater" containment capacity than current systems.

But no permanent solution is expected until the first of two relief wells is completed in order to inject drilling fluids into the gushing well and then seal it for good with cement.

The first relief well is expected to intersect the busted well by the end of July but it will take days or weeks -- until about mid-August -- to plug the leak, Wells said.

BP's backup plans include stationing nearly 400 boats between the Deepwater Horizon site and the Gulf Coast and more than 50 aircraft to spot and scoop up the additional oil that would flow into the Gulf.

In Pass Christian, Mississippi, cleanup crews in yellow reflective vests fanned out across the white sand beach, scooping tar balls from the water's edge with shovels and rakes under a punishing sun.

"It's a travesty," said Michael Howson, 48, who left his home in Chicago six weeks ago to work as a safety supervisor with the crew.

He's seen dead porpoises, turtles, pelicans, crabs, sea turtles and patches of oil as big as a car wash up on the beach.

"It's terrible they haven't been able to cap it yet," he told AFP. "It's destroying the beaches, it's destroying the wildlife and it's destroying the people."

Oil has now washed up on beaches in all five Gulf states -- Texas, Louisiana, Mississippi, Alabama and Florida -- forcing the closure of fishing grounds and threatening scores of coastal communities with financial ruin.