Turkish broadcaster NTV said there were still high levels of methane in the mine air which raised the chances of another explosion and complicated rescue efforts.

Poor safety records

Al Jazeera's Anita McNaught, reporting from the mine, said the methane gas provided a number of complicating factors.

"The blasts are usually extremely large, extremely high temperature.

"Not only do they collapse tunnel walls - they melt metal supports, they suck the oxygen out of the air, they replace it with carbon monoxide.

"It would be quite a miracle if any of these 30 remaining men were retrieved intact from what happened."

Mothers and wives of the miners have been anxiously waiting near the entrance of the mine.

Eight other workers, who were trapped in the elevator after the explosion, were rescued on Monday, with at least two brought to the local hospital for treatment for gas poisoning.

The Black Sea region is Turkey's largest coal producer, with output primarily focused on fuel for domestic heating needs.

Many of Turkey's mines have poor safety records, with more than 2,700 workers killed in mining accidents since 1955.

The worst such accident happened in 1992 when 263 workers were killed in a gas explosion in a mine in Zonguldak where the current rescue operation is under way.