Four people have been killed and eight left injured after a collapse of Severnaya coal mine in Vorkuta, Russia.
The mine is owned by Vorkutaugol, an integral part of Russian steel and mining company Severstal.
An initial investigation suggested that the incident occurred due to methane emissions, with a blast at the mine trapping more than 110 workers underground.
Russia's Ministry of Emergency Situations carried out laboratory analysis as part of the investigation.
Rescue operations at the mine are in place although a ground collapse and strong fumigation is making it more complicated, the company said.
So far, Severstal has safely evacuated 80 people to the mine's surface and is continuing with its efforts to evacuate the remaining 26 miners.
Severstal CEO Vadim Larin said: "On behalf of everyone at Severstal, I would like to express my deepest condolences to those affected by this tragic incident, particularly the friends and families of our valued colleagues who lost their lives.
"The safety of our employees is our number one priority, we have invested significantly into safety equipment and procedures at Vorkutaugol in recent years."
The company is working with the authorities and an investigation is underway to determine the cause of the incident.