The far-right Italian politician Matteo Salvini has threatened to “evict” the national government if his coalition triumphs in two regional elections.

Italian newspapers reported a “boom” in turnout – up 23% in the wealthy northern region of Emilia-Romagna and 10% in Calabria, in the south – by midday, as voters headed to the polls in elections that could precipitate a return to national power for Salvini’s League.

The former deputy prime minister, whose party was ejected from government last summer after he failed to force snap elections, has flouted campaign silence rules with a flurry of tweets.

In one, he wrote: “First we’ll send them home [in Emilia-Romagna and Calabria] on Sunday and then we’ll give the government of [migrant] landings, taxes and handcuffs an eviction notice.”

Emilia-Romagna and Calabria are both led by the centre-left Democratic party (PD), which formed a precarious national alliance with the Five Star Movement (M5S) in September after Salvini’s unsuccessful gambit.

Polls before the blackout period began gave Salvini’s group, which includes the smaller far-right Brothers of Italy and Silvio Berlusconi’s Forza Italia, a clear lead in Calabria.

The race in Emilia-Romagna is much tighter, with the League’s candidate, Lucia Borgonzoni, neck and neck with the PD’s incumbent regional president, Stefano Bonaccini.

However, a defeat for the PD there would be more crushing as the region has been a leftwing bastion since the end of the second world war.

Triumphs for Salvini’s coalition would further destabilise the PD-M5S alliance and could lead to a government collapse, as it would probably increase tensions between the coalition partners, with more MPs from both defecting as their faith in the alliance dwindles.

That could bring forward general elections that would favour the League, given its leading position in national polls.

The resignation of Luigi Di Maio as M5S leader last week has added to the turmoil and Nicola Zingaretti, who leads the PD, may also come under pressure to quit if his party loses the regional votes.

Support for each party has waned since the two came together, with the PD polling at 18% and M5S at 16%. The League has maintained a steady lead at about 33%, while support for Brothers of Italy, which is led by Giorgia Meloni, has risen to 10.9% in recent months.

Salvini and Meloni have led energetic campaigns across both regions, with their pledges to defend Catholic values, repel unwanted immigration, increase security and cut taxes resonating widely.

“If you give us a hand, on Monday we’ll go and ask for early elections to give this country a strong, coherent government,” Meloni said at a closing rally in Ravenna, Emilia-Romagna, on Friday.

The League has already made serious inroads in the region as voters switched allegiances in recent years, managing to capture several small towns before winning its first major city, Ferrara, last June.

The Salvini coalition also came first in Emilia-Romagna in national elections in 2018 and again in European parliamentary elections last May.

The League’s latest campaign has featured familiar toxic traits, with Salvini sparking an outcry after marching up to a block of flats on the outskirts of Bologna last week and, encouraged by laughing supporters, ringing the bell of a Tunisian family’s home to ask over the intercom if they were drug dealers. At the same time, he has posed for selfies with African immigrants who he claimed were supporters.

Many say the League’s true rival in Emilia-Romagna is the Sardines, a movement that emerged in Bologna in mid-November in reaction to Salvini’s threat to “liberate” the region from the left. The movement has managed to mobilise thousands to demonstrations across the country. “The real match is between the Sardines and Salvini,” Mattia Santori, one of the movement’s founders, said on Thursday.