A 1 -by-5 mile sheen of crude oil mix has spread after a deepwater oil platform burned for more than a day after a massive explosion and sank into the Gulf of Mexico, media reported on Thursday.

An explosion and fire on an offshore drilling platform off Louisiana's coast Wednesday leaves seven workers badly hurt and 11 missing. [Chinanews.com]

The sink of the Deepwater Horizon could unleash more than 300,000 of gallons of crude a day into the water, creating a potential for a major spill as search for the 11 workers missing in the blast continued, the Coast Guard said.

Coast Guard teams had been combating the fire on the Deepwater Horizon, which suffered the blast about 10 p.m. Tuesday off the Louisiana coast and continued burning since then, the Coast Guard said.

The rig had deteriorated badly throughout the morning, authorities said.

Built in 2001, the semi-submersible rig is owned by Houston-based Transocean, the world's largest offshore drilling contractor, and has been under lease by BP (NYSE:BP) since 2007. It was drilling but was not in production.

(1 mile = 1.609 metre)