Crews in the US have raced to protect the Gulf of Mexico coastline as a remote submarine tried to shut off an underwater oil well that's gushing 42,000 gallons (160,000 litres) a day from the site of a wrecked drilling platform.

If crews cannot stop the leak quickly, they might need to drill another well to redirect the oil, a laborious process that could take about two months while oil washes up along a broad stretch of shore, from the white-sand beaches of Florida's Panhandle to the swamps of Louisiana.

The oil, which could reach shore in as little as three days, is escaping from two leaks in a drilling pipe about 5,000 feet (1,500 metres) below the surface. The spill has grown to more than 1,800 square miles (4,700 square kilometres).

Winds and currents can change rapidly and drastically, so officials were hesitant to give any longer forecasts for where the spill will head.

The oil began spewing out of the sea floor after the rig Deepwater Horizon exploded on April 20 and sank two days later about 40 miles (65 kilometres) off the Mississippi River delta.

Eleven of the 126 workers aboard at the time are missing and presumed dead; the rest escaped. The cause of the explosion has not been determined.