LANZHOU, Aug. 27 -- The death toll has risen to 15 after a bus carrying 61 people collided head-on with a truck on a highway in northwest China's Gansu Province, local authorities said on Wednesday.

The new casualties came after two injured passengers were confirmed dead, said a statement from the government of Guazhou County, where the accident happened on Tuesday.

A total of 48 people are receiving medical treatment, including two in critical condition, said the statement.

The tragedy occurred 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.

Thirteen of those killed were aboard the overloaded 55-seater bus, which was carrying seven children.

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.