A Bulgarian oil worker was missing on Wednesday after an offshore rig belonging to Italy's Saipem sank off the coasts of Angola and Democratic Republic of Congo after the seabed collapsed. Saipem said the drilling rig began tilting on Monday and fell on Tuesday in water 40 metres (131 feet) deep near the mouth of the Congo River. "The emergency procedures were promptly activated last night to ensure the evacuation of the personnel on board," Saipem said in a statement.