Preliminary information indicates the explosion at Zasyadko mine was caused by methane gas, according to DAN, the official news agency for the self-proclaimed Donetsk People's Republic (DPR).
"This did not happen because of shelling," an emergency services official told the news agency.
The explosion occurred just before 6 a.m. local time, when 230 people were at the mine, the official website for separatist-controlled Donetsk city said.
Of those, 157 were evacuated in the initial hours after the blast, including 14 injured and one dead, according to the website. Fifteen rescue teams are working at the scene, it said.
Yatsenyuk: Separatists are not allowing rescue teams in
Zasyadko mine is one of the most dangerous in terms of methane in Ukraine, according to the Ukrainian news agency Ukrinform, which reported that 240 people had died at the mine since 1999 -- 101 miners were killed in a single accident in 2007.
Ukrainian Prime Minister Arseniy Yatsenyuk, speaking at a Cabinet meeting, accused the pro-Russian separatists who control the area of denying Ukrainian rescue teams access to the site, Ukrinform reported.
He urged Russia to tell the separatists to allow in the rescue workers.
"You took millions of Ukrainians in Donetsk and Luhansk hostage and are now brutalizing miners' families by not letting in help," Ukrinform quoted him as saying.
Ukrainian President Petro Poroshenko also called for rescuers to be allowed in.
"I demand Ukrainian rescue workers and investigators to be granted access at the site of the tragedy," he tweeted.
However, DPR representative Denis Pushilin said Ukraine had not offered help with the rescue, and the DPR will ask Russia or separatist authorities in Luhansk for help if needed, according to the separatists' news agency.
Separatist leader Aleksandr Zakharchenko issued an order to close the mine a month ago, but managers ignored the order because the mine legally belongs to Ukraine, Ukrinform cited the separatist news agency as saying.
A shaky ceasefire is currently in place in Donetsk and the neighboring Luhansk region, the center of a months-long conflict between pro-Russian separatists and Ukrainian government forces.