Rescue workers have found the remains of 33 miners killed in a gas explosion taking place Thursday afternoon at a small colliery in Yangyuan City of Shanxi Province, north China, an official said Friday.

Vice-Mayor Chen Jiguang said the rescue operation was halted because of the thick toxic gas down in the shaft shortly after the explosion until 3 a.m. Friday when rescuers could go down again.

The accident occurred at around 4:20 p.m. Thursday in Daxian Sankeng Colliery, when 71 miners were working underground.

After the explosion, 38 of the miners were hoisted to the ground, 28 miners were found dead and five others remained missing.

The coal mine, which produces 150,000 tons of coal a year, was a licensed one, the provincial supervision center of coal mine safety said.

The cause of the accident is under investigation.