XI'AN -- Four people were killed and one was injured when a house collapsed in Xi'an, in Northwest China's Shaanxi province, local authorities said.

The collapsed part of the house in Xichao, a western suburb of Xi'an, was an illegal structure under construction, according to the city municipal government.

Villagers surnamend Tian and Zhang intended to build another three floors on top of an original three-storey structure. The fifth floor of the house collapsed around 9 am Thursday and triggered the collapse of the west side of the building.

Rescue work continues as police further investigate the cause of the collapse.