Fifteen people were killed and 48 injured on Tuesday afternoon when a bus carrying 61 people collided head-on with a truck on a highway in northwest China's Gansu province.

The accident occurred at about 12:20 when the bus broke through the central partition, veered into the opposite lane and crashed into an oncoming semi-trailer truck on a highway in Guazhou County in the city of Jiuquan, the county police department said in a statement.

By 01:00 on Wednesday, thirteen of the dead were passengers on the bus, and two were in the truck. Of the injured, six are in critical conditions. The injured have been rushed to two hospitals.

The overloaded 55-seater bus was carrying nine children.

Pictures show the truck leaning to one side, while the front of the bus is smashed to pieces. The site of the accident was so damaged that it has been cordoned off for repair work, according to local police.

The bus, owned by Xinjiang Siping Commercial Trade Co., Ltd in Urumqi, capital of the far western Xinjiang Uygur Autonomous Region, was en route from Miquan in Urumqi to Guyuan in Ningxia Hui Autonomous Region.

According to Wang Fuguo, director of Dongsheng Bus Station where the bus set out from, there were 56 people (52 passengers and three drivers) on the bus when it left the bus station, and the bus must have picked up more passengers halfway.

An investigation into the case is under way.