Rescue efforts are underway after a section of a major bridge collapsed in the US city of Baltimore. A Singapore-flagged container ship, the Dali, had collided into a pillar of the Francis Scott Key Bridge. Two people have been rescued so far, with one in serious condition. The fire department has called it a "mass casualty event", with search operations looking for seven individuals. Officials earlier said there could be as many as 20 people in the water. Simon Marks reports from Washington DC.