A four-storey building under construction in China's northwest and a factory wall in an eastern city collapsed in separate accidents, killing at least 14 people and injuring eight others, state media said Sunday. Eight workers were killed and three others were injured when the residential building toppled Saturday in Xi'an, the capital of northwestern Shaanxi province, the official Xinhua News Agency said. More than 300 firefighters, police and medical workers were sent to the scene, it said. A community official said substandard construction material may have caused the collapse, Xinhua reported. It said police were searching for two contractors who fled the scene. Separately, Xinhua said six people were killed Sunday when the wall of a factory, also under construction, fell in eastern China's Shandong province. Five people were injured, two of them severely, in the accident in Qingzhou city, it said.