Deep snow, heavy wind, mechanical vibration and a rapid temperature rise were blamed for an avalanche that killed at least four in northwest China's Xinjiang Autonomous Region, a meteorologist said on Saturday.

Between March 6 to 12, heavy snow hit the Guozigou area where the accident happened three times. A maximum wind speed of 20 meters per second at an altitude of 3,000 meters increased the avalanche risk, said Gao Minghua, the observatory head at the Kazak Autonomous Prefecture of Ili.

The mechanical vibration of machines in the tunnel in such bad weather accelerated the vibration in the mountain. This, coupled with a rapid temperature rise since early March that speeded up the thaw and added weight to the snow, caused the avalanche, Gao said.

Experts suggested that construction be avoided in snow-hit mountainous areas in winter.

Six workers were pulled out of a tunnel on Friday after being trapped for 25 hours by the avalanche and one body was found. Fifteen others, buried in drifts of more than 50 meters deep blocking the entrance of the tunnel construction site, remained missing, according to the latest investigation result on Sunday night.

"More than one million cubic meter of snow in the tunnel is the biggest block for the rescue," said Yan Cheng, an armed police official.

The avalanche occurred at around 10?AM on Thursday when five workers were in the tunnel and a team was about one kilometer away on their way to the project in Ili.

The five workers dug a narrow passage through the thick snow over the past day, enabling rescuers outside to get them out. They were under emergency treatment in a local hospital. Doctors said the five were weak, but not in a critical situation.

Eight huge excavators were still digging at the site of the accident.

A moderate snow was expected to hit the region on Sunday and Monday, which will dampen the rescue effort, according to a weather forecast from the regional observatory on Saturday afternoon.

The tunnel is at a remote area known as "Guozigou". It is about 500 kilometers from Urumqi, the regional capital.

(Xinhua News Agency March 17, 2008)