Two-thirds of the 600,000 people quarantining are potential voters.
Portuguese voters under COVID-19 quarantine will be able to visit their polling stations on January 30 but have been urged to do so late in the day.
The ballot later this month will elect 230 lawmakers to the Republican Assembly, Portugal's parliament.
The Interior Ministry announced on Wednesday that voters under quarantine "will be able to leave their place of confinement on this day, strictly, to exercise their right to vote."
Authorities are calling on COVID-19 positive voters to attend their polling station during its last opening hour so as to minimise contact with other voters.
During the municipal elections in September and the presidential elections last January, which were held under strict general lockdown and when the country was hit hard by the pandemic, this possibility was not available.
"The problem we had in the previous elections has been magnified because we now have many more people infected," Interior Minister FranciscaVan Dunem said.
Omicron sweeps through
Portugal recorded more than 52,500 new infections on Wednesday -- a new pandemic-high blamed on the spread of the Omicron variant.
Some 600,000 people are under quarantine, two-thirds of whom are potential voters out of a total of 9.3 million registered voters in Portugal.
Portugal currently ranks 5th in the European Union in the number of new cases detected in the last two weeks but it is only 17th in terms of the number of deaths relative to its population thanks to its record vaccination coverage -- 82.9% of its 10.3 million population is fully vaccinated.
Authorities have opened early voting and about 200,000 voters, including outgoing Prime Minister Antonio Costa, have already registered to vote this coming Sunday, a week before the official election date.
The ballot comes two years ahead of schedule, after parliament in November rejected the minority Socialist government's 2022 state budget and the country's president, Marcelo Rebelo de Sousa, called a snap election.
The state budget is particularly important now because it sets out how billions of euros in European Union aid to recover from the pandemic will be spent.
The left expected to win
Costa's Socialist Party (PS) is projected by a Pitagorica poll released on Thursday to come out on top with 39% of the vote, followed by the Social Democrats (PSD) with 30%.
But the Socialists could again fall short of an overall majority, forcing it once again to seek support from its left-of-centre allies, the Left Bloc and the Portuguese Communist Party, which are projected to respectively secure 5.1% and 5.3% of the vote, to pass legislation in parliament.
The parliamentary votes of those two parties helped keep the Socialists in government, consigning the centre-right PSD, the country's other major party, to the opposition.
The election could see a rise in the influence of smaller parties, including the populist Chega! (Enough!) which earned one seat in parliament in 2019 but could far exceed that this time. Chega! is currently polling third at 7.2%.
Portugal's death toll of 19,400 is much lower than in neighbouring Spain where 91,437 people have lost their lives. Authorities have attributed the low fatality to early measures including border closures and strict lockdowns.
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