Chileans will head to the polls on Sunday for a presidential runoff in which the favourite is a Donald Trump-inspired candidate who has pledged to build a wall along the country’s borders to keep migrants out.

José Antonio Kast, 59, an ultra-conservative former congressman who has built his campaign on a promise to expel tens of thousands of undocumented migrants, faces Jeannette Jara, 51, a former labour minister under the current centre-left president, Gabriel Boric, 39.

Jara finished the first round ahead, with 26.9% to 23.9%, but while she was the unified candidate of a leftwing coalition, rightwing contenders, including Kast, together took more than half of the votes.

For that reason, and given recent polling, Kast – the son of a Nazi party member, an admirer of the dictator Augusto Pinochet and a staunch Catholic known for his opposition to abortion and same-sex marriage – is widely expected to rule Chile for the next four years.

One novelty in this election, however, has led analysts to urge caution in calling his victory: for the first time in more than a decade, voting is once again compulsory.

In past elections, about a third of the country’s 15 million voters did not usually take part. “These 5 million people are more distrustful of politics,” said Claudia Heiss, a political scientist at the Universidad de Chile, who argued that in November’s first round, this “new” electorate was attracted by rightwing populist promises and voted against the ruling coalition.

But Heiss says this voting bloc’s behaviour in the runoff remains unpredictable: another candidate, economist Franco Parisi, 58, appeared to benefit from their backing. Parisi, who was running for a third time, still presented himself as an “outsider” and secured a surprising third place with 20% of the vote.

“Parisi appealed to an audience of young men who generally had no political engagement,” said Rossana Castiglioni, a political science professor at the Universidad Diego Portales.

Now, she said, it is difficult to know where Parisi’s votes will go, since, unlike the other defeated rightwing candidates, he did not endorse Kast in the runoff. Instead, he stuck to his campaign slogan of “neither fascist nor communist”, and many of his voters may end up spoiling their ballots as a form of protest.

Still, “if we trust the polls, everything indicates that Kast should be the winner”, said Castiglioni.

Heiss said that Kast has benefited from a wave of public “paranoia” on security and migration. Chile’s immigrant population has doubled in the past decade, fuelled by about 700,000 Venezuelans forced to leave their country amid its economic collapse.

“There is a fear linked to the emergence of new forms of crime that weren’t common here – such as contract killings, kidnappings and extortion – linked to the arrival of foreign organised crime groups, but they are not the bulk of migrants coming to Chile,” said Heiss.

“Heightened fear has created fertile ground for penal populism and iron-fist policies,” she added.

In a presidential debate, Kast twice claimed that “1.2 million people are murdered each year in Chile”, a completely unrealistic figure. Despite an increase in recent years, the country actually registers about 1,200 homicides a year, still making it one of the safest in Latin America.

Like many rightwing leaders across the region, Kast describes himself as an admirer of El Salvador’s president Nayib Bukele, who has imprisoned at least 2% of his country’s adult population as part of a controversial crackdown on gangs. “Every Chilean voting today, if Bukele were on the ballot, would choose Bukele,” he said in another debate.

Jara has also presented her own version of an “iron fist” policy, saying security is her “top priority” and promising to build five new prisons and expel immigrants convicted of drug trafficking.

While Jara says she wants to register the roughly 330,000 undocumented migrants through biometric identification, Kast has given them an ultimatum to leave before the next president takes office on 11 March or be expelled “with only the clothes on their backs”.

Migrants are a central focus of his platform, which includes a Trump-inspired plan to build detention centres and 5-metre-high walls, electric fences and 3-metre-deep trenches as well as an increased military presence along the border, particularly in the north, on the frontier with Peru and Bolivia.

Despite Kast’s clear praise and references to Trump, the US president has not expressed support for his Chilean follower, unlike in other Latin American elections this year – including Argentina and Honduras, where analysts and local politicians criticised Trump for outright interference.

Even without any sign of support from his political lodestar, Kast has continued to revere Trump and his actions. Asked in the debate whether he would support a US ground intervention in Venezuela, the ultra-conservative responded positively, using the motto of Chile’s national coat of arms: “By reason or by force.”