AlQa'dah 23, 1434, Sep 29, 2013, SPA -- Five people have died and 21 others have been left injured after a passenger bus collided with a semi-trailer in northwest China's Gansu Province on Sunday evening, authorities said. The bus with 33 people on board overturned after the collision at 5:20 p.m. on the Lianyungang-Khorgos highway in the city of Wuwei, Xinhua quoted to the Gansu Provincial Public Security Department as saying. Four passengers on the bus were killed immediately, and another died after medical treatment failed. Twenty-one people have been hospitalized, police said. The cause of the accident is under investigation.