'Top-kill' operation underway to fix BP oil leak

BP has started pumping heavy mud into the leaking Gulf of Mexico well in the company's boldest attempt yet to plug the gusher that has spewed millions of gallons of oil over the last five weeks.

The so called 'top kill' method has worked above ground but has never before been tried 5,000 feet beneath the sea.

The energy giant hopes the mud can overpower the steady stream of oil, but BP's Chief Operating Officer Doug Suttles said it would be at least 24 hours before officials know whether the attempt has been successful.

Company officials peg its chance of success at 60 to 70 per cent.

The company eventually wants to inject cement into the well to permanently seal it.

A live video stream of the operation shows pictures of the blowout preventer and a mix of oil and mud coming out of the broken pipe. But a weak spot in the blowout preventer could blow under the pressure, causing a brand new leak.

Frustration with BP and the federal government has grown as efforts to stop the leak have failed.

More than 100 miles of Louisiana coastline have been affected by the oil spill. Experts predict the state will lose more pristine coastline as a result of this tragedy than the combined loss from four recent devastating hurricanes - Katrina, Rita, Gustov and Ike.