An oil rig in the Gulf of Mexico that caught fire after an explosion on Tuesday has now sunk, the US coastguard has said. The coastguard is still looking for 11 missing workers after the blast at the Deepwater Horizon rig. There has been no sign of the group despite efforts by patrol boats through the night and an aerial search that resumed on Thursday. The other workers on the rig, off Louisiana, were evacuated to the US. The aerial search had resumed at dawn but there has been no sign of those missing.