SEVEN people, two of them emergency services personnel and five municipal contract workers, were killed when the walls of a four-metre deep trench collapsed on them in Potchefstroom on Tuesday. Town clerk Hannes Botha says municipal contract workers were digging a sewerage trench to lay new pipes when the weight of the digging machine caused one side of the trench — four metres deep and two metres wide — to collapse, burying a contract worker who was already inside the trench. A second worker, who was trapped under mud, was pulled out of the trench and resuscitated by paramedics. Emergency services personnel were called in to assist the trapped worker. During the rescue bid all the trench walls collapsed, killing in all two emergency personnel and five municipal contract workers.