A giant oil slick, formed as a result of the Deepwater Horizon offshore drilling rig explosion last week, is expected to hit the US Gulf Coast shoreline this weekend as The White House and Congress launch separate probes into the worst offshore incident in nearly a decade.

The leaking well, 5,000ft under the ocean surface off the Louisiana coast, has created an oil sheen and emulsified crude slick with a circumference of about 600 miles, covering about 28,600 square miles, according to the US Coast Guard.

Eight underwater robots are being used to activate a cut-off valve on the ocean floor to stop the oil flow.

The US Coast Guard is considering deliberately setting fire to the petroleum on the sea’s surface to stop the spread of oil.

Forecasters predict that a shift in winds could push the spill inland to the Louisiana coast by this weekend, which will also affect the coasts of Alabama, Mississippi and Florida.

BP, the owner of the well, is spending $6m a day on a massive on-sea clean-up effort involving dozens of ships and aircraft, according to Reuters.