There has been a "serious incident" at one of Europe's deepest mines with fears of a gas explosion, the local MP has said.
The incident occurred overnight at Boulby mine in East Cleveland, which produces potash, an important ingredient in fertilisers.
Labour MP Tom Blenkinsop, who represents Middlesbrough South and East Cleveland, said: "There has been a serious incident, believed to be a gas explosion, and we are waiting for further details about what has happened."
There was an underground fire at the mine in April, which left seven workers affected by smoke and they were taken to hospital for checks.
Last year the company announced job losses in a "significant restructuring" of its operations, including moving from producing potash to polysulphate fertiliser.
The mine is 1,400 metres deep and its tunnels go far out under the North Sea.