Greek far-right extremists have assaulted Thessaloniki’s mayor, Yiannis Boutaris, throwing into sharp relief the threat posed by fascist forces in Europe.

The mayor, one of Greece’s most prominent liberal voices whose visionary policies have helped transform the country’s second-largest city, was recovering in hospital after the attack late on Saturday.

Boutaris, 75, was attending an event commemorating the first world war massacre of Black Sea Greeks by Turks when his attackers forced him to the ground, punching and kicking him.

Yiannis Boutaris is helped after the attack. Photograph: EPA

He was rushed to hospital with head, back and leg injuries. “They were hitting me everywhere. Kicks, punches, the lot,” he told the nation’s state-run news agency. “It was a despicable attack but I am well.”

Footage from the scene shows the mayor being heckled before the assailants hurled bottles at him and kicked him in the head and legs. As he is hastily escorted into his car, some of the attackers attempt to smash the vehicle’s windows.

The assault was quickly blamed by the government and opposition on fascist supporters in Greece.

Golden Dawn, one of Europe’s most violent ultra-nationalist organisations, is the country’s third biggest political force and, in an age of austerity and profound polarisation, is again on the rise.

After a period of relative calm coinciding with the trial of much of its leadership on charges of running a criminal gang, the group appears to have been re-emboldened, attacking immigrants and leftist activists with apparent impunity. A senior member was imprisoned after confessing to the assassination of the popular anti-fascist Greek rapper Pavlos Fyssas in 2013.

The assault on Boutaris has now taken matters to another level. The mayor of Athens, Giorgos Kaminis, described the “fascist attack” as “a direct threat to democracy and society”, and asked that the town hall’s municipal council meet for an emergency session on Monday to discuss it.

Long considered a maverick, Boutaris, who has several tattoos and has spoken about his alcoholism, came into Greek politics from the business world after decades running his family’s highly successful wine company.

Anti-conformist, bold and outspoken, he has openly clashed with Golden Dawn through dogged promotion of policies that have won plaudits abroad but nationalist anger at home.

In his eight years as mayor, Boutaris has been credited with single-handedly turning around Thessaloniki’s fortunes by promoting its once vibrant multicultural past.

Under his stewardship, the city has celebrated being the birthplace of Kemal Atatürk, the founder of modern Turkey, and embraced its Jewish heritage with works under way to build a Holocaust museum to commemorate the estimated 50,000 Jews who perished during Nazi occupation.

“The museum will be a beacon against racism and fascism,” he proclaimed earlier this month in Berlin.

Tourism from Turkey and Israel to Thessaloniki has soared dramatically. Boutaris, who has long advocated solving the name row over Macedonia, the tiny Balkan state north of the city, has more than once declared that his aim “is not to be liked but to be useful.”