<p><br /> BP is about to lower a huge metal box over a Gulf of Mexico oil spill in a last-ditch attempt to head off an environmental disaster.<br /> </p><p><br /> One of the company's wells blew out two weeks ago, 40 miles off the coast of Louisiana, sinking the Deepwater Horizon rig.<br /> </p><p><br /> Millions of gallons of oil have seeped out into the sea, and the slick is expected to hit the coast of the southern United States within days.<br /> </p><p><br /> A ship carrying the giant white-painted box has arrived at the site of the spill. BP says it is hopeful the 98-tonne device will help to contain the oil and funnel it to a tanker.<br /> </p><p><br /> The US is to carry out a controlled burn of some of the leaked oil to stop it from getting closer to the shore of Louisiana and Mississippi.<br /> </p><p><br /> A sheen of oil has washed ashore on uninhabited Freemason Island in the Chandeleur chain. It is the first confirmed report of oil reaching the US shoreline.<br /> </p>
