Two miners are dead and an estimated 16 others are trapped after a coal shaft collapsed on Tuesday in northwest China's Shaanxi Province.

The emergency response office of the provincial government said the accident happened at around 11:16 a.m. at the state-owned Huisen Liangshuijing Coal Mine in Shenmu County, 600 kilometers north of the provincial capital of Xi'an.

At least 28 workers were working underground when the accident happened and 12 were rescued. However, two died in hospital of what the doctors described as "gas poisoning".

Rescuers are searching for the trapped miners, but they must first clear the blocked tunnels.

Some rescuers said heavy smoke and dust in the tunnel hampered the operation. The collapse might release huge amounts of the toxic gas in the coal layers, which would be extremely dangerous to those trapped.

Local government officials would not rule out the possibility of survivors.

Work safety officials are investigating the cause of the collapse.

Wu Dengchang, vice governor of Shaanxi, has gone to the mine to oversee the rescue work.