A colliery blast that killed 29 miners in Chengcheng County of the northwestern Shaanxi Province at the end of October was caused by smoking in the shaft, said local authorities on Thursday.

Investigation results showed that the ventilation system was blocked before the accident, which caused concentration of gas.

Wu Dengchang, vice governor of Shaanxi, ordered a check-up of coal mines and tightened management. "We must draw a lesson from this severe accident," he said.

The explosion took place in the Yaotou mine at about 8 p.m. on Oct. 29. Only seven of the 36 workers in the pit at the time escaped.

The mine, with a complete set of valid licenses, has an annual capacity of 330,000 tonnes.

(Xinhua News Agency November 27, 2008)