Six people - most of them rescuers - have been killed in a new explosion in a mine in northern Russia where 26 miners went missing after an accident three days ago.

All of the missing miners are now also presumed dead, officials said on Sunday.

"Six people died, five of them rescuers," Anton Kovalishin, a spokesman for the emergencies ministry in the Komi region where the Severnaya mine is located, told the AFP news agency.

Separately, Emergencies Minister Vladimir Puchkov said the 26 missing miners were most likely also dead.

The accident at the Severnaya mine was Russia's worst mining accident in years.

On Thursday, four miners were killed and 26 went missing after a collapse at the Severnaya mine in the city of Vorkuta within the Arctic Circle.

Authorities launched a massive search operation involving hundreds of rescue workers and until now had refused to declare the missing miners dead.

But Puchkov, speaking to reporters on Sunday, said the 26 could not have survived.

"Unfortunately, we are forced to acknowledge that all the conditions at that section of the mine would not allow a person to survive," he said, in remarks broadcast by LifeNews television channel.

Puchkov earlier said rescuers had risked their lives during the search operation working in tough conditions, including almost zero visibility, gas-polluted air, and rubble.

President Vladimir Putin has tasked the government with creating a special commission to investigate the accident.

In 2010, 91 people - miners and rescuers - died after a methane explosion at the Raspadskaya mine in the Siberian region of Kemerovo.

In 2007, 110 people died at the Ulyanovskaya mine in the Kemerovo region in the country's worst mining accident since the Soviet Union collapsed in 1991.

Source: AFP