A man has died in an underground accident at a potash mine in East Cleveland - one of Europe's deepest.
Rescue teams at Boulby potash mine had been dealing with a problem involving the release of gas, Owners ICL UK said.
Worker John Anderson, 56, died following a "sudden and powerful release of gas" in the early hours, the firm said. There was no explosion.
Middlesbrough South and East Cleveland MP Tom Blenkinsop has called for an investigation in the wake of the death.
Other employees who were in the mine at the time were safely evacuated, a spokesman said.
The mine makes potash for fertilisers and employs about 1,100 people.
In April, seven workers were taken to hospital after a fire broke out at the mine, which is 1,400m deep and has tunnels that go far out under the North Sea.
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A company spokesman said: "The incident is believed to have involved a gas blowout - a sudden and powerful release of gas."
Her Majesty's Mines Inspectorate has been informed.
"Company staff will be offering all possible support to the man's family. All other workers in the mine at the time of the incident were safely evacuated."
Mr Blenkinsop said: "The miner who died in the explosion was one of my constituents who lived in East Cleveland.
We cannot allow this death to go unmarked. Over the last decade and a half, the mine has been a safe working environment, certainly compared to years past where accidents were more frequent."
"However, in the space of just a few months we have seen two tragic incidents. I am concerned that this must not become a pattern.
Mines legislation requires a full investigation, and I need to be reassured that this will indeed happen."
"I would also want to be reassured that recent redundancies at the mine have not altered day to day working practices to the extent that risk may have been allowed to creep back in."
Mr Blenkinsop said he was intending to meet senior mine management from ICL Ltd and the mine's unions.
Cleveland Police said they were called to the mine at 05:20 BST and confirmed the man's death. Officers remain at the scene.