The emergency services and the mine's rescue team are working at the scene following the blast in the early hours of Friday.
A man has been killed after a "sudden and powerful release of gas" at one of Europe's deepest mines.
The mine in Boulby, East Cleveland, produces potash, a key ingredient in making fertiliser.
It is 1,400m deep and stretches out far under the North Sea.
ICL UK, which operates the mine, said the gas "blow-out" took place in the early hours of Friday.
All other workers were safely evacuated from the site and mine inspectors informed of the blast, the company said.
The emergency services and the mine's rescue team are working at the scene and an investigation has been launched into what happened.