Will Ukraine polls bring tensions to a head in the east?
Thick white smoke billows from the chimneys, flames from the furnace dart across the factory. The Avdiivka bauxite plant fuels Ukraine's huge steel industry. Nestled on the country's eastern edge, metal production still drives the Ukrainian economy.
But something else has ignited here in recent weeks: the spark of separatism, which now risks engulfing the entire region.
After Ukraine's southern province, Crimea, was annexed by Moscow in March, pro-Russia groups in eastern Ukraine took their cue.
Insurgents led a rebellion against Kiev and called a contentious referendum here. They claim 90% voted in favour of independence, a figure the West considers a farce.
Declaring a "People's Republic of Donetsk" and a similar one in the city of Luhansk, they have vowed to block the Ukrainian presidential election on Sunday from taking place in this region.
Thursday's attack on a Ukrainian army checkpoint near Donetsk, in which at least 14 soldiers were killed, appeared to make their point known. It was the deadliest assault on the military since this conflict began, leading the interim prime minister to talk of "war declared on Ukraine".
But the company that runs the steel and iron factories - Metinvest - is hitting back at the separatists. Employing 140,000 people, its owner, Rinat Akhmetov - Ukraine's richest man - has talked of "genocide" by armed pro-Russian groups, whom he calls "bandits and looters".
Yuriy Ryzhenkov, Metinvest's CEO, worries that if the attempted secession continues, "the world won't recognise this territory and so our exports will stop and people will be out on the streets".
"If we cannot sell our products to market, if we cannot attract financing," he tells me, "it would mean huge unemployment and closed factories. The only way to save the industry - and this region - is to stay within Ukraine."
Officials of the self-styled Donetsk Republic say it's too late - and that the people here have voiced their desire to split. The referendum results they quote are widely believed to be inconceivable and, in reality, the region is deeply split.
There is considerable animosity to Kiev, fed by a Moscow propaganda machine that calls for protecting ethnic Russians from a "fascist" Ukrainian government.
The rhetoric from Kiev, denouncing "terrorists" in the east and leading botched military assaults here, has hardened the hostility. But there is also a considerable number - the vast majority, according to a survey by Pew Research, who want to stay within Ukraine, albeit with more local powers.
At a pro-Russia rally in central Donetsk, one of the separatist leaders, Denis Pushilin, is whipping up the crowd, calling for men to sign up to fight "the Ukrainian occupiers".
There are just a few hundred people there - "because people didn't know about this meeting", he assures me. "I myself just found out it was taking place."
I ask whether the ballot will take place here. "It's very hard for us to hold an election for a neighbouring country," he says. "We can't guarantee the safety of those who vote. We shouldn't open up polling stations and risk people's lives."
I put it to him that the outside world sees him and his creation as illegal. "We voted for the Donetsk People's Republic with an absolute majority," he tells me. "And that is what has legitimised our country. It's more important than recognition by the outside world."
To make their presence known, armed separatists continue to roam the region.
In some areas, like Sloviansk, they're in near-total control. But in Donetsk city, men in balaclavas wielding AK47 rifles and rocket-propelled grenades appear sporadically. It is a warning shot to those intending to vote on Sunday.
And there are still plenty who want to take part. Election posters are up in Donetsk and on the streets of the city, we found many determined voices.
"It's very important that we use this voting as a step forward for peace and the integrity of our country," says Olexiy, strolling in the sunshine with his wife and daughter. "The armed men may try to scare us, but I hope it won't stop me."
"This election will allow us to raise our voices for Ukraine," says Svitlana, a charity worker, "because it will stop Putin saying that the government in Kiev is not legal".
But the separatist groups are managing to disrupt the process.
Election officials and voter lists have been seized at gunpoint and some buildings used for the poll forced to close.
As we arrived at one election office, the staff decided to evacuate after they got word that a colleague elsewhere had been abducted.
Open campaigning is also too risky. The Donetsk office of one candidate, Sergey Tigipko, was attacked this week with a petrol bomb. Countless officials have been threatened by phone or letter.
"We can't promote the election on the streets," says Natalia Skepko, from Mr Tigipko's team. "We mustn't even say 'Glory to Ukraine' or show state symbols. At best we'd lose our health. At worst, we'd lose our life."
What fate lies ahead for a divided eastern Ukraine? There are fears that the tensions of recent weeks will come to a head on Sunday, when two visions of the future collide: one trying to have a say in a united Ukraine, while the other breaks apart and reaches out to Russia.
The choice between these two paths runs far deeper than which candidate to elect - if the poll can even take place in this troubled territory.