An estimated 7,000 people have crammed together in the northern Italian city of Modena as part of a growing “sardines” movement against the politics of the far-right leader, Matteo Salvini, in which opponents attempt to beat the numbers he draws to his rallies.

Protesters converged under the rain at Piazza Grande on Monday night as the former interior minister campaigned in the city before crucial regional elections in Emilia-Romagna, a leftwing stronghold.

It followed a gathering of an estimated 12,000-15,000 people in Bologna last Thursday night amid a heavy downpour to counteract the launch of a campaign by the League candidate, Lucia Bergonzoni, to vie for the presidency of Emilia-Romagna as part of an alliance with the smaller far-right party Brothers of Italy, and Silvio Berlusconi’s Forza Italia.

The next demonstration is planned in the coastal city of Rimini on Sunday, where Salvini will inaugurate the League’s regional headquarters.

Salvini has pledged to “free Emilia-Romagna from the left” in the elections on 26 January. The administration is under the control of the centre-left Democratic party, which is ruling nationally alongside the Five Star Movement.

The sardines protests were devised by four friends from Bologna as a riposte to Salvini’s boasts about filling Italy’s squares with supporters. His coalition launched its campaign at an indoor sports arena in Bologna with the capacity to accommodate about 5,700 people.

“The limit was already defined and so we decided to try to gather 6,000 people at Piazza Maggiore,” Andrea Garreffa, one of the four friends, said. “In the end, between 12,000 and 15,000 people came. There were people of all ages, packed together like sardines in the rain. Their presence was a message of opposition to the hate that the far right is trying to bring to Emilia-Romagna.”

The images of packed squares in Bologna and Modena were shared widely on social media, prompting similar initiatives in Florence and Benevento, a town in the southern Campania region.

“Salvini said that Emilia-Romagna needed to be free of the left,” added Garreffa. “But the whole of Italy was freed from dark powers at the end of the second world war. We don’t need to be freed, we are a free people and as free individuals we are gathering together as the basic values of participation and democracy are at stake.”

Salvini has mocked the movement, saying in Modena last night: “Next time, I’ll go to the square with them.”

Emilia-Romagna is one of Italy’s top industrial regions and the Salvini coalition has been targeting the business community as part of its campaigning. “I prefer businesses to sardines,” Salvini added. “With all due respect there are businesses in difficulty. I come to propose things.”

Businesses in the region have been particularly irked by a national government plan to impose a tax on plastic packaging.

Bergonzoni, the former deputy culture minister, will compete in the elections against the PD president, Stefano Bonaccini. Bonaccini is polling ahead of Bergonzoni.

Meanwhile, Salvini is again being investigated for “kidnapping” migrants whom he refused to allow to disembark from an NGO rescue ship in August 2018.