Waving colourful flags, hundreds of campaigners took to Lisbon's streets on Friday ahead of Portugal's weekend snap election, with polls giving the opposition centre-right an edge after eight years of Socialist rule, and huge gains for the far-right.

Support for the Democratic Alliance (AD) has inched up in the final days of the campaign to hit 32.6 percent against the Socialists' 27.9 percent, according to Radio Renascenca's poll aggregator.

But analysts warned the results of Sunday's general election remained wide open due to the large number of undecided voters.

Far-right party Chega, led by former television football commentator Andre Ventura, is tipped to more than double the 7.2 percent it won in the last election in 2022.

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Portuguese parliament / © AFP

That scenario would make it a kingmaker in a new parliament and add momentum to Europe's swing to the populist right.

Angela Loureiro, a 51-year-old lawyer, brought her 16-year-old daughter to an AD street rally near a fruit and vegetable market in Lisbon's upscale Alvalade neighbourhood.

"I am tired of these incompetent people who have governed us. It is unthinkable that this country has regressed in eight years," she told AFP as other AD supporters waved orange party flags around her.

The election was called after Socialist leader Antonio Costa, 62, resigned in November following an influence peddling probe that involved a search of his official residence and the arrest of his chief of staff.

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Portugal's outgoing Prime Minister Antonio Costa, seen here pointing to new Socialist party leader Pedro Nuno Santos, has defended his record / © AFP

Costa himself has not been accused of any crime but he decided not to run again.

Under Costa, unemployment has dropped, the economy expanded by 2.3 percent last year -- one of the fastest rates in the eurozone -- and public finances have improved.

But surveys indicate that many voters feel Costa's government squandered the outright majority it won in 2022 by failing to improve unreliable public health services and education, or address a housing crisis that has sparked noisy street protests.

"The positive macroeconomic context is not reflected in the quality of life of the Portuguese because of inflation, low wages or problems with state services," said political scientist Marina Costa Lobo of Lisbon's Social Sciences Institute.

- 'Safe harbour' -

The Socialists' new leader, 46-year-old former infrastructure minister Pedro Nuno Santos, has defended the government's record even as he acknowledges it could have done better in some areas.

Addressing the crowds at a rain-soaked rally in Baixa Chiado, one of Lisbon's most iconic neighbourhoods, he said the Socialist party was a "safe harbour" that would "govern for all Portuguese, unlike our adversaries".

The AD has vowed to boost growth by cutting taxes, and to improve public education and healthcare.

At a final rally at Lisbon's main bullring, the party's leader, 51-year-old lawyer Luis Montenegro, said the AD offered a "safe change".

But if the polls are accurate and the AD comes first but falls short of an outright majority, it could struggle to form a government.

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Teenagers hold flyers depicting the leader of far-right party Chega, Andre Ventura, which read 'Portugal needs a clean-up' / © AFP

Montenegro has steadfastly refused any post-election agreement with anti-establishment party Chega, which has said it would demand to be part of a rightist coalition government in exchange for parliamentary support.

But "this may prove the only way for the centre-right party to govern," said Agnese Ortolani, principal economist at the Economist Intelligence Unit.

Chega's "potential inclusion in or support for an AD-led right-wing coalition would shift policy further to the right," she added.

- 'Same thing' -

Founded in 2019, Chega calls for tougher measures to fight corruption, stricter controls over immigration and chemical castration for paedophiles. Its campaign billboards feature the slogan: "Portugal needs a clean-up".

It is the first far-right party to win representation in Portugal's parliament since a military coup in 1974 toppled a decades-long rightist dictatorship.

Ventura on Friday said that his party was "as legitimate as the others".

"The Socialists and the AD represent exactly the same thing and only a strong vote for Chega will allow us to put an end to the two-party culture in Portugal," he added.