Hundreds more were still believed to be trapped in the mine in Soma, about 480 kilometres (298 miles) southwest of Istanbul. The explosion, which triggered a fire, occurred shortly after 3 pm (1200 GMT) on Tuesday.
"We are heading towards this accident likely being the deadliest ever in Turkey," Energy Minister Taner Yildiz told reporters at the scene.
Prime Minister Tayyip Erdogan declared three days of national mourning.
The disaster highlighted Turkey's poor record on worker safety and drew renewed opposition calls for an inquiry into a drop in safety standards at previously state-run mines. The International Labour Organization ranked the EU candidate nation third worst in the world for worker deaths in 2012.
Yildiz said the fire was still burning underground, which miners said was hampering the rescue operation and denting hopes of finding more survivors. A pall of smoke hung above the area.
The blast happened during a shift change, leading to uncertainty over the exact numbers of miners trapped inside. Yildiz earlier said 787 workers were in the mine at the time and that the death toll may rise further.
"I have to say that our hopes are dimming in terms of the rescue efforts," he said.
Rescue workers pumped oxygen into the mine to try to keep those trapped by the blaze alive, as thousands of family members and co-workers gathered outside the town's hospital. Many of the dead had suffered carbon monoxide poisoning, Yildiz said.
Some 93 people were rescued, including several rescuers, and 85 of them were being treated for their injuries, the Disaster and Emergency Management Presidency said in an email.
One relative told broadcaster CNN Turk that his 15-year-old nephew was among workers still trapped inside the shaft.
A cold storage warehouse, usually used for food, and freezer trucks served as makeshift morgues as hospital facilities overflowed. Medical staff intermittently emerged from the hospital to read the names of survivors being treated inside, with families and fellow workers clamouring for information.
Teams of psychiatrists were being pulled together to help counsel the families of victims. Paramilitary police guarded the entrance to the mine to keep distressed relatives at a safe distance from the rescue effort.
There were calls on social media for protests in front of the Istanbul headquarters of Soma Komur Isletmeleri, the operator of the mine. The company said in a brief statement late on Tuesday that there had been "a grave accident" caused by an explosion in a substation but gave few other details.
Erdogan cancelled a visit to Albania, scheduled for Wednesday, and is instead going to the site of the disaster, his office said. President Abdullah Gul also cancelled a trip to China scheduled for Thursday in order to travel to Soma.
At Istanbul's Taksim Square, two left-wing opposition newspaper vendors read out headlines to silent morning commuters. "Turkey is a graveyard for workers", and "This wasn't an accident, this was negligence."
Turkey's rapid growth over the past decade has seen a construction boom and a scramble to meet soaring energy demands, with worker safety standards often failing to keep pace.
Its safety record in coal mining has been poor for decades, with its deadliest accident to date in 1992, when a gas blast killed 263 workers in the Black Sea province of Zonguldak.
The Labour Ministry said late on Tuesday its officials had carried out regular inspections at the Soma mine, most recently in March, and that no irregularities had been detected.
But Hursit Gunes, a deputy from the main opposition Republican People's Party, said a previous request for a parliamentary inquiry into safety and working conditions at mines around Soma had been rejected by the ruling AK Party.
"I'm going to renew that parliamentary investigation demand today. If (the government) has been warned about this and they did nothing, then people will be angry, naturally. The opposition warned them. But there's unbelievable lethargy on this issue," Gunes told Reuters.
The ILO in 2012 said Turkey had the highest rate of worker deaths in Europe and the world's third-highest. In the mining sector, 61 people died in 2012, according to the ILO's latest statistics. Between 2002 and 2012, the death toll at Turkish mines totalled more than 1,000.