A powerful explosion ripped through a building in a northern Chinese city on Monday, killing seven people and injuring scores more. Media reports said the blast in Yulin, which destroyed or damaged nearby buildings including a hospital, may have been caused by explosives illegally stored in the building. The official Xinhua news agency said dozens of fire-fighters were sent to the scene in Shaanxi province, and rescuers were hunting for survivors who may be trapped in the rubble.