A spontaneous bus combustion last month, which claimed 11 lives in Zhaoyuan County, northeast China's Heilongjiang Province, was caused by heat protection stuffing in the engine cabin, said investigators Sunday.

A spokesman with the investigation team said that the stuffing, mostly cotton and polyurethane foam, had been put in the cabin by the bus driver to keep the engine warm in subzero temperature.

He said the inflammable materials caught fire when the engine turned hot.

Ten of the 17 people on the bus were killed on the spot. An injured passenger died in hospital on December 4.

The spokesman said that families of the dead and injured in the accident had been compensated. The investigation was continuing to seek responsibilities.