The incident occurred in rebel-controlled Donetsk city's Zasyadko coal mine - one of eastern Europe's largest and scene of a similar incident on January 11.
"When the power went out, there were 496 miners underground," a Donetsk region emergencies ministry official told AFP by telephone.
"But the miners are now making their own way out to safety. The ventilation systems are all working and their lives were never in danger."
More than 300 miners were trapped in the same pit for a few hours on January 11.
The nine-month war in east Ukraine between pro-Russian militants and government forces has claimed nearly 5,100 lives.
Fighting around the rebel stronghold Donetsk intensified this month after a brief lull and the daily death toll is again reaching levels last seen at the height of the war in August.
Rebel leaders last week pulled out of peace talks with the Western-backed government in Kiev and vowed to seize new territory that could expand their reach over most of Ukraine's industrial east.
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