Russian President Vladimir Putin expressed his condolence to the families of those killed. A day of mourning would be observed in the Khanty-Mansiysk district on Monday, Xinhua news reported.
A bus carrying 29 children aged between 12 and 14 and three adults collided with a truck on a highway linking two Siberian oil towns, Khanty-Mansiysk and Tumen.
The children who belong to an acrobatics team were returning from a competition in another city when the accident occurred, local emergencies service reported.
The cause of the accident was not known. Low visibility and bad weather conditions could have been a reason, it said.