The movement was formed last week by four friends from the northern city of Bologna in response to Salvini’s boasts about filling Italy’s squares with supporters.

Salvini is looking to lead a resurgent right to its first victory in Emilia-Romagna in the January 26 regional vote and has said if the left loses power in the northern region then it should also quit central government and give way to a national ballot.

Experts say Emilia-Romagna, a traditional leftist stronghold, could fall to the League and its right-wing allies following successes in other regional votes, most recently in central Umbria last month.

Polls also say the right would win a national vote, with the League seen as Italy’s most popular party.

But between 12,000 and 15,000 people answered last Thursday’s protest call, squeezing together like sardines in the rain in Bologna’s main square to denounce Salvini and his anti-immigrant, Italy-first rhetoric.

“To those who shout the loudest, we are responding by being as silent as fish, but in a shoal, packed one next to the other,” Mattia Santori, one of the organisers, said.  

“There are more of us than them.” 

Following the unexpected success of the Bologna rally, a new protest was called for Monday in the nearby city of Modena, where around 7000 demonstrators defied downpours in silent protest.

Using “sardine” as a tag on social media, demonstrations were also announced on Tuesday across the region, including Reggio Emilia on Saturday and the coastal city of Rimini on Sunday, where Salvini will inaugurate the party’s regional headquarters.

The movement also started to extend beyond Emilia-Romagna, with “sardine” rallies called for the Tuscan city of Florence, the Lombard capital of Milan, the Sicilian capital of Palermo and the town of Benevento, in Campania.

The ruling Democratic Party (PD) and its coalition partner, the anti-establishment Five Star Movement (M5S), have kept their distance from the movement, although PD leaders have welcomed the protests.

The M5S was born out of a peaceful street protest in Bologna in 2007.