US Air Force planes are preparing to spray oil-dispersing chemicals off the coast of Louisiana as the operation to tackle a huge slick is stepped up.

Fears of an ecological disaster along the southern US coast have mounted as oil from the sunken rig in the Gulf of Mexico began to wash ashore.

Animal rescue groups along the coast started to receive their first patients – seabirds coated in thick, black oil.

Worsening weather conditions are threatening to hamper the operation.

The US National Weather Service said strong winds could push the oil into inlets, ponds and lakes in south-east Louisiana over the weekend.