ZHENGZHOU - The death toll from a gas outburst at a colliery in Central China's Henan province Wednesday has risen to 12, local authorities said Friday.

There were five confirmed deaths and seven people trapped underground on Thursday. The bodies of the seven trapped miners were discovered at 6 am Friday at Xingyu Colliery in Xuzhuang township in the city of Dengfeng, according to the city publicity department.

The accident happened around 5 pm Wednesday when workers were expanding a pipe way in the colliery, causing the gas outburst.

Thirty-nine of the 51 people underground at the time of the accident managed to escape.

An initial investigation indicates that the accident was triggered by human error.

Xingyu Colliery, built in 1975, is licensed and has an approved annual capacity of 330,000 tonnes.

The colliery had temporarily suspended production to check hidden dangers on Dec 12 and had resumed operation on Dec 29 with government approval, according to Chen Zhilong, vice mayor of Dengfeng.