An explosion in a nickel mine in China’s Henan Province has killed at least seven people and left four seriously injured.

The Government of Tanghe County in Nanyang City, where the accident took place, confirmed that an explosion hit a ventilation shaft in a mining pit run by Shidai Mining Industry.

Fourteen workers were exploring mining resources at the time of the explosion.

The rescue headquarters said an investigation into the cause of the blast is underway, according to China Daily.

Shidai Mining is engaged in exploring and mining non-ferrous metals such as nickel and copper.