Workers in Italy joined a general strike on Friday, not for better pay or conditions, but in solidarity with the people of Gaza.

Large crowds took to the streets of multiple cities amid a growing wave of protest across Europe at Israel's bombardment and blockade of the Gaza Strip.

Italy's Interior Ministry says up to 400,000 protesters came out in total in 29 locations; trade unions claim the number was four times that.

Anger intensified this week when the Israeli military boarded a flotilla of boats full of European politicians and activists and stopped them delivering food and medical aid to Gaza, where UN-backed experts have confirmed famine in Gaza City and its surrounding areas.

Israel dismissed the flotilla as a publicity stunt. There were more than 40 Italians on board.

Italy's hard-right Prime Minister Giorgia Meloni criticised the general strike, arguing that it would not advance the Palestinian cause and only hinder Italian people trying to go about their lives. She suggested the unionists just wanted a long weekend.

Her deputy, Matteo Salvini, called the strike illegal, announced without sufficient notice, and threatened sanctions.

Large numbers turned out regardless, behind banners with slogans like Stop the Massacre and Hands off the Flotilla!.

In several cities, including Milan and Bologna, there were clashes, with protesters throwing stones at police then being sprayed with tear gas.

There were protests in other European cities, too, from The Hague to Madrid.

Here in Rome the main march was large, but peaceful. Governments, especially the Italians, are not taking action against what is happening in Gaza, said university teacher Francesca, explaining why she'd joined the walkout.

Students at Sapienza University where she works are staging sit-ins at several faculties.

At the end of the day, as unionists, students and activists were still marching in multiple cities, the four Italian politicians who'd been detained on the aid flotilla to Gaza landed back in Rome to warm receptions.

More than 40 fellow Italians remain in custody.