Lines of workers gather outside Donetsk's Chelyuskintsev coal mine waiting to start their shifts, despite artillery fire around them.
The entrance to the pit is guarded by armed rebels and pro-separatist graffiti adorn the fences nearby.
Vitaly Khristich is one of hundreds of workers at this and other local mines that go down in the pit every day, braving the fighting outside and being unpaid for months.
Without them the shaft would get flooded and could simply be lost as an energy source.
One kilometre up, above ground, Ukrainian government firing positions dot the fields around.
About 55 percent of all coalmines in Ukraine are situated in a relatively small area controlled by pro-Russian rebels who declared independence in May and have been fighting government troops for months.
The frontline that separates the warring parties cuts off the mineral wealth of the Donetsk region from energy capacities, endangering the future of the region and the energy security of Ukraine.
Heavy fighting and electricity blackouts have paralyzed the work of dozens of mines in the region, Ukraine's industrial heartland.
The rebels threaten to stop sending coal to Kiev, while the Ukrainian government could cut off the electricity supply generated at a power station on the other side of the frontline.
Many separatist combatants in Donetsk are local miners, and the pro-rebel sentiment among this workforce is strong.
Miners like Khristich don't hide their sympathies.
"Coal will be ours and Donetsk People's Republic will take care of it. It will be used where it's needed, but not to oligarchs, who made money on this coal," he said.
The Chelyuskintsev mine is government owned but who actually runs it is anyone's guess.
Despite the war it has been shipping all the coal it produces to the state-owned distributor, but it is not receiving government financing.
Around 100 Chelyuskintsev miners have joined the fighters and others said they will vote in the November 2 rebel election as long as there is no heavy fighting outside.
Mine director Vasily Dancha says he was "advised" to take down the Ukrainian flag a few months ago.
But he would not fly the rebel flag, either. Whoever pays the miners will get their flag on a pole, he says.
Coal output in the Donetsk region dropped by 20 percent in January-September compared to the same period last year, to 22 million tons, forcing the Ukrainian government to consider importing it from abroad - an unprecedented step for this energy-rich country.
Kiev has already contracted to buy 1 million tons from South Africa.
Dancha says workers want to work and know how to make the mine productive so the profit prospects are good as long as there's investment.
"All coal mines have to be renovated, so they can provide materials to raise production of metal, electricity and chemicals," he says.
The troubles in the east could threaten the mining industry and livelihoods across the country.
Ukraine is already experiencing a 30 percent coal shortage at power stations, the country's Energy Minister said earlier this month.
Ukrainian officials were concerned by reports that there rebels were thinking about starting to export the coal, to the Crimean Peninsula, which was annexed by Russia in March.
Rebels may threaten to stop shipping coal to Kiev, but the Ukrainian authorities hold cards of their own.
Most coalmines in rebel-held areas are powered by a hydro-electric plant in the town of Kurakhove, which is under government control.
"If they keep it," Dancha said, "it will be an important leverage for them to use."
The plant in Kurakhove in turn runs on coal from the Donetsk mines, a neat illustration of the indissoluble mutual reliance both sides will find hard to overcome.
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