As Ukraine’s second-largest city of Kharkiv came under a barrage of Russian air and rocket attacks on Tuesday morning, 29-year-old Taras Kovalchuk ventured out to take his dog Yoko for a short walk.

Shortly after leaving his apartment in the city’s central Freedom Square, his phone started to buzz, as a flurry of alerts from local authorities warned of imminent air raids.

A friend messaged asking if he was OK, and a push notification informed him that a missile had hit the square.

“Until the missile destroyed my flat, I was strongly convinced that I would stay in Kharkiv,” he told Al Jazeera.

Taras Kovalchuk’s apartment in Freedom Square was left badly damaged

Kovalchuk walked back to his apartment, opposite the regional administration building that was hit by a Russian military attack not long after sunrise, to a scene of devastation.

Closed-circuit television footage showed a fireball engulfing the street in front of the Soviet-era building. An emergency official said the bodies of at least six people had been pulled from the ruins, and at least 20 other people were wounded.

It was not immediately clear what type of weapon was used or how many people were killed. Ukrainian officials said at least 11 people were killed. President Volodymyr Zelenskyy said there were dozens of casualties and accused Russia of war crimes.

“What I saw was the craziest thing in my life,” Kovalchuk said. “I could not imagine that a human being could behave like that with another human being.”

Central Café, the local coffee house where he had spent many mornings across the years, had been wrecked by the blast. Upstairs, the windows in his flat had burst and doors had flown off their hinges. Glass and debris carpeted the floor, and furniture lay overturned.

Central Café, the local coffee house, has been wrecked by the blast

Kovalchuk grabbed the evacuation bag he had prepared in case of emergency when Russia launched its invasion of Ukraine on Thursday and set off for a 40-minute-long walk to the train station, navigating a ravaged city he barely recognised amid the constant sound of shelling.

Tuesday marked the first time the Russian military hit the centre of Ukraine’s second-largest city, whose population of 1.4 million is mostly Russian-speaking. Residential neighbourhoods have been shelled for several days.

Some 87 Kharkiv apartment buildings have been damaged, and several parts of Kharkiv no longer have water, electricity or heating, Mayor Ihor Terekhov told Ukrainian TV channels.

Anton Gerashchenko, adviser to the Ukrainian interior minister, said that “practically, there are no areas left in Kharkiv where an artillery shell has not yet hit.”

The Russian military has denied attacking civilian targets, despite reports that it is shelling residential buildings, schools and hospitals. It says it is only targeting Ukraine’s military infrastructure, air defence and air forces with high-precision weapons.

Kharkiv has put up stiff resistance to Moscow’s advance, with Ukrainian forces capturing a unit of Russian troops that entered the city during the weekend.

Starting on Monday, Russian forces unleashed a barrage of multiple-launch rocket fire against residential neighbourhoods, killing at least 10 civilians, including three children, and injuring at least 40, according to local officials.

Terekhov, Kharkiv’s mayor, said every fourth person in the city has relatives who live on the other side of the border. “But the city’s attitude to Russia today is completely different to what it ever was before,” he said in an online video statement.

“We never expected this could happen: total destruction, annihilation, genocide against the Ukrainian people – this is unforgivable.”

On Wednesday, clashes erupted after Russian paratroopers landed in Kharkiv, the Ukrainian military said.

Kovalchuk has fled the city and found refuge at a friend’s home. Just last week, he was writing for a digital magazine and blogging about travels. Now, he can barely contain the anger the invasion of his home country and the destruction of his city have awakened in him.

“We can’t call [Russians] humans – humans don’t act like them with the civilians,” he said. “The world has to stop Russia now.”