Portugal's Socialist Party leader, Pedro Nuno Santos predicts last-minute voter support ahead of Sunday's election will help secure a win in the face of the far-right party's mounting ambitions.

Santos has headed up the centre-left party for the past two months following the resignation of Prime Minister Antonio Costa amid a corruption investigation.

Speaking to Reuters news agency following a campaign rally in Setubal, Santos stated: "We are very confident, the reactions we have had in the last few days have been extraordinary and we will continue to work until the last day to win, to have a big victory."

Voting for the Socialist Party "is the best way to stop the far-right in Portugal and its influence on any future government," he went on to add, in reference to the populist party, Chega that is hoping to become a decisive force for the centre-right Democratic Alliance (AD) and securing a role in government.

According to the majority of opinion polls, the Democratic Alliance is marginally in front of the Socialists yet falling short of a working parliamentary majority. According to analysts, either could receive the most votes, as around 20% of voters remain undecided.

However, the combined right, which includes the far-right Chega, will likely have a parliamentary majority. Despite this, the Democratic Alliance has thus far dismissed any possibility of entering into an agreement with Chega, Reuters reports.

Furthermore, Santos said the Socialist Party is "in the best position" to maintain "the financial and budgetary stability that was achieved" with the reduction in public debt under 100% of GDP and a budget surplus.

"We have our public accounts balanced and this is an asset that we want to preserve, because it is very important for us to continue moving forward...in salaries, pensions and public services," he stated.

Santos has advocated for a targeted approach to incentives in specific sectors with significant potential to drive economic transformation while claiming the Democratic Alliance's proposal of universal tax cuts is "irresponsible."