It was like one of the illicit apartment concerts from Soviet days, only with better cocktails. Dozens of young people packed into a basement room, singing along to classic Russian and Ukrainian tunes strummed out by a rotating cast of guitarists.

They had gathered to say goodbye to Izba Chitalnya ("village reading room"), Donetsk's hippest cafe-bar, which was closing due to poor business as a result of the ongoing conflict in eastern Ukraine. When they belted out the first lines of the beloved No One Will Hear by the Russian band Chaif – "I haven't heard from my old friends, it's sad, and the daily newspaper leaves my soul empty" – it was almost as if they were singing about the turmoil in their own city.

It has been three months since pro-Russian protesters seized the Donetsk regional administration building, sparking the most serious separatist conflict in the former Soviet Union since it fell apart in 1991. At least 423 people have died, according to a June estimate by the UN.

The upshot for Donetsk, once a city of a million people, is as much psychological as physical. Tens of thousands have fled and hundreds of businesses have closed. A surreal atmosphere pervades the city centre, where ATMs have run out of cash, shops shut early, and it is not uncommon to see men with machine guns posted outside a sushi restaurant or behind the wheel of a city ambulance. People strive to live as normally as possible: on one memorable occasion this month when a firefight endured for hours near the regional police headquarters, locals blithely went about their business in nearby districts as if they couldn't hear the shooting.

"The people are already very scared, and the spiritual condition here is not entirely good," the mayor, Alexander Lukyanchenko, told the Guardian. He said around 30,000 people had left the city since the start of the conflict, and many more had left on a kind of early summer holiday. In addition, 12% of small and medium-sized businesses had closed or significantly scaled back their work since the start of the year, and 8,207 employees had lost their jobs, he said. But such things are hard to count, and the real numbers may be much higher.

The mayor's office itself provides a neat microcosm. Lukyanchenko and his team still turn up for work, trying to play a delicate balancing act between the anti-Kiev rebels and the central government that still provides pensions and other social payments.

The mayor says his staff work in "unbelievably hard" conditions. The militia who seized city hall in April have left the building, but no one knows for how long. Rebels driven from the separatist town of Slavyansk this weekend are now reportedly regrouping in Donetsk. A precarious city just became even more precarious.

The centre of Donetsk, which was once packed with cars and pedestrians, is extremely quiet and empty. "We're walking around as if we were in a tiny village," said Vitaly Samarin, who owns a flat-rental business. "It used to be hard to find a place to park, now you can park wherever you want."

Samarin has reduced his pool of rental apartments from 53 to 12 since the conflict started, and his income has fallen by at least 60%. His main clientele, people on long-term business trips, are no longer coming to Donetsk. That includes some members of the world's oldest profession: prostitutes from the Donetsk region who were renting three of his apartments skipped town after rebels – who ostensibly promote conservative values – arrived and flung ink at them, he said.Samarin would like to leave, but doesn't want to give up his business or his home, a flat he bought for $130,000 (£75,000) that he said was now worth $40,000 due to the collapse of the housing market. "The majority who went voted yes [in a May referendum on self-determination]. Now, judging by conversations I've had, many are disappointed because it got worse, they've been fired, the stores aren't open, the banks aren't open," he said.

Indeed, it's difficult to find a cash machine with any cash, and grocery and convenience stores continue to reduce their hours or close altogether. A string of department stores on Artyoma Street, the city's main drag, have closed, with huge "50% off" sale signs still adorning the windows of three of them. One of those still open, Four Seasons, was advertising discounts of 60%. Its manager, Alexander, said customer flow was half that of last year.

A pair of distributors delivering milk and beer to stores said that although there was no shortage of food, the variety was limited because not all shipments got through to the warehouses. Foreign-made cigarettes are in short supply, and residents have had to resort to less popular local brands. An employee at a pharmaceutical distributor said foreign-made medicines were also hard to find because shipments had been disrupted, most likely by the maze of Ukrainian and rebel checkpoints, he said. In particular, cancer medicines and antibiotics are lacking.

The entire city is a ghost town after dark, due as much to a general sense of apprehension as to a loosely enforced 10pm curfew. Cafes and restaurants typically close around dusk, with custom desultory and staff eager to get home early on less frequent public transport. Nightclubs that were once packed with patrons echo pitifully. It's hard to find a bar in which to watch the World Cup.

The owner of Izba Chitalnya, who asked that his name be withheld, said he had to close the cafe because he could no longer make the rent. His main customers – middle-class young people, most of whom are pro-Ukrainian – had been the first to leave Donetsk, he said. "We have a lot more former clients in Lviv and Kiev than in Donetsk."

Vitaly, a journalist who lost his job when his television channel cut staff after the conflict started, said residents of the far-flung Petrovsky district where he lives tried not to leave home after dark, for fear that shelling might start from nearby government troop positions or that a rebel patrol might come by. This week, rebels burst into a slot machine parlour shortly after curfew and beat up the tipsy patrons, he said. "There are too many people with weapons around who decide your fate very quickly," he said. "People's eyes have gotten less kind … they don't know who to trust."

Vitaly continues to bring his collection of Soviet cameras, photographs and other paraphernalia to an outdoor flea market, where the afternoon sun gleamed off a Lenin bust that he had repainted to look like a "'90s gangster" with a moustache and a polka-dot tie. A woman nearby selling oil paintings by her daughter, an art student, said people were only spending money on absolute necessities, not art.

Anya, a flower seller near the interior ministry office where one officer was killed in a shootout on Monday, said people were barely buying flowers any more. A woman who came into the shop during an interview – the first customer all day, she said – was trying to hide the fact that they were celebrating in such a time of crisis. "Put them in a bag, please, so people don't see," the customer asked.

Donetsk was once a hotbed of rival opinions, with clashes between pro-Russian and pro-Ukrainian protesters leaving one man dead in March. But pro-Ukrainian activists and members of the local football ultras, who along with Kharkov ultras originated the "Putin is a dickhead" song that has since become a nationwide cultural meme, have been fleeing for their own safety. A member of the Donetsk ultras who would identify himself only as Dima moved to Lviv in mid-May. He said people in Donetsk had grown "harsh and angry" during the conflict, and it was dangerous even to speak in his native Ukrainian on the street.

"We have comrades who disappeared and we don't know where they are to this day," he said. "Our addresses, the addresses of those who supported revolution in Donetsk, the addresses of football fans, including mine, were freely accessible in internet, with our home phone and parents' names."

Foreign students from poor countries, who have been coming to Donetsk in large numbers since Soviet times, are also leaving. Merdan, a student from Turkmenistan who declined to give his last name, estimated that up to half of those living in a dormitory of mostly foreign students had left due to the conflict. But many remain, including Abdullah Rang, a student from Iraq who said he wasn't planning to leave. "Why should I be afraid? I've seen a lot worse," he said.