The company plans to put the funnel in place on Thursday, the BBC reported. The funnel plan is the first large scale effort BP has been able to make thus far to stop the estimated 5,000 barrels of oil leaking from the bottom of the sea.

BP authorities, who are under the obligation of US law to clean up the spill that occurred when the rig it was leasing from Transocean  caught fire on April 20, and blew up and sank two days later, are grasping a straws on how to staunch the high pressure flow.

The 98-ton, dome-topped box being built by steel workers will be connected to a drill ship and lowered to the sea floor above the geyser of the leak.

BP has never deployed such a structure at a depth of 5,000 feet (1,500 metres) and difficulties may occur, the company said late  Tuesday.

“There’s no guarantees,” BP boss Tony Hayward told AP news agency.

“We’ll undoubtedly encounter some issues as we go through that process. But if that was a good outcome, then you would have the principal leak contained by the early part of next week,” Hayward said.

BP has accepted it is “absolutely responsible” for cleaning up the spill caused by a blast on the drilling rig. But doubts remain among Gulf residents, especially fisherman, that this claim will extend to compensation for lost business.

More than 200 class action and private suits have been filed again BP. Transocean, the Deepwater Horizon rig’s owner, is also facing hundreds of suits in what US President Barack Obama Sunday called a “potentially unprecedented” environmental disaster.

It is estimated that the clean-up could cost BP up to $15 billion (£10 billion), and it’s stocks have plunged more than 15 percent since April 22.

BP and Transocean are bickering loudly and publicly over who is at fault for the accident.

Schwarzenegger terminates offshore drilling for California

Californian Governor Arnold Schwarzenegger has withdrawn his support for a plan to expand oil exploration off that state’s coast, saying he has changed his mind about the safety of oil platforms in the Pacific Ocean.

After seeing television pictures of the Gulf of Mexico spill, he asked: “Why would we want to take that kind of risk?”

Technical challenges

The 40ft (12m) funnel being built on BP funding resembles a primitive space rocket with a hole on top to channel oil through a pipe from the sea floor to the surface where it can be collected on a barge, Reuters news agency reports.

The funnel is under construction at Golden Meadow, near Port Fourchon in southern Louisiana, by Wild Well Control, a company that specialises in controlling oil fires.

A team of 25 people is working around the clock on the funnel, marine engineer Jason Holvey told the agency.

In theory, the system should collect 85 percent of the oil rising from the sea floor. While the precise location of the leak is known, work will have to be carried out in the face of severe technical challenges, not least beng the softness of the sea floor, the Reuters reported.

Asked by Reuters if he was confident it would work, BP spokesman John Curry said: “We sure hope so – if not, we will keep trying other options until something does work. I think we have some great engineers and they have worked very hard.”

The funnel will have to be tested before it can be shipped to the spill site. A second, back-up funnel is also under construction, AP said.

Holvey said similar containment devices had been used in the Gulf before, but in shallow waters. They were used, for instance, after Hurricane Katrina to channel oil to the surface that had spilled from platforms.

Vice-grip of US pressure on BP

The US government has been putting pressure on BP to act quickly.

In a BBC interview, Hayward dismissed talk of a rift between BP and US officials, saying an “incredible co-operative relationship” had been established with the federal authorities. An estimated 5,000 barrels of oil have been leaking into the Gulf of Mexico each day since the rig sank 12 days ago.

Some oil has washed ashore, but officials say the bulk of the slick remains a few miles from the Louisiana coastline.

Other efforts being made by BP, according to Mr Hayward, include using undersea robots to work on the safety valve, called a blowout preventer, which failed, allowing the oil to escape, and drilling a new well to help relieve the pressure and stem the flow from the rupture.