The blast, caused by a build-up of methane gas, occurred more than 1,000m (3,280ft) below ground in the Zasyadko mine in the eastern Donetsk region.

A massive rescue operation is underway, but a fire and damage to ventilation systems are hampering rescuers.

Hundreds of frantic relatives rushed to the mine in search of their loved ones.

At least 350 of the more than 450 miners who were below ground when the explosion happened at 0300 (0100 GMT) have been rescued, emergency officials said.

About 25 of those rescued have been taken to hospital, many suffering from methane inhalation.

Ukraine's emergencies situations ministry says 63 bodies have been found.

The chances of finding alive many more of those missing are "small", the head of the mine's trade union, Yuriy Zayats, said.

PM 'grieves'

Prime Minister Viktor Yanukovych is at the scene of the accident, one of Ukraine's worst mining disasters in several years.

In pictures: Deadly blast

"I am grieving with all of Ukraine," he said in a statement, according to AFP news agency.

Earlier he told reporters there had been a cave-in at the accident site, and that fire and smoke were also obstructing rescuers.

Miners' family members gathered at the mine entrance, trying to find news of their men.

"I detest them, these mines," a middle-aged woman searching for a relative told AFP.

Periodically an official has been reading aloud the surnames of those confirmed dead, to the anguished cries of relatives.

One miner, Vitali Kvitkovski, told the BBC that just before the explosion, he had checked his instruments and the methane levels seemed normal.

"I was walking to the coal layer. There was a bang, the temperature surged, and [there was] thick dust. You could see absolutely nothing," Mr Kvitkovski said.

A criminal case has been opened into the accident, the Ukrainian Prosecutor General's Office told news agency Itar-Tass. It said the Donetsk regional prosecutor was visiting the scene.

Three days of mourning have reportedly been declared by the head of the regional administration.

Safety 'ignored'

The country's coal mines are among the most dangerous in the world with a high number of fatalities from accidents.

Miners' pay varies according to the volume of coal produced, giving them an incentive to ignore safety procedures that would slow production, a union official said.

"Everyone tries not to pay attention to small problems in the safety equipment," Anatoly Akimochkin told AFP.

"The pay system is one of the biggest causes of our accidents."

One miner was killed on Saturday in a cave-in at the Lenin mine, also in the Donetsk region.

A gas leak at the Zasyadko coal mine, one of Ukraine's largest, killed 13 miners and injured dozens more in September 2006.

Twenty miners were killed in an explosion at the same mine in 2002.

And 80 people were killed in another explosion at the Barakova coal mine in Luhansk in 2000.