LISBON -- Portuguese voters return to the polls on Sunday for the second round of the presidential elections, the first such runoff in roughly four decades, in a contest between the center-left and the far-right.

In the runoff, Socialist Party candidate Antonio Jose Seguro, who led the first round with approximately 31 percent of the vote, will face off against Andre Ventura, leader of the far-right Chega party, who placed second with 23.49 percent. Chega emerged last year as one of the main political forces in Portugal's parliament.

Portugal operates under a semi-presidential system, in which the president and the prime minister share executive power. While the president does not manage day-to-day government, the office holds significant authority, including the power to dissolve parliament and call a snap parliamentary election in times of crisis. The president can also block laws, but parliament can override the veto.

Opinion polls released in recent weeks have indicated a clear lead for Seguro in the runoff. A survey by the Center for Studies and Opinion Polls at the Catholic University of Portugal showed the Socialist candidate with 70 percent of voting intentions, compared with 30 percent for Ventura.

Polls have also pointed to a high rejection rate for Ventura, estimated at around 60 percent of voters.

The campaign, however, has been overshadowed by severe winter weather that has hit Portugal in recent weeks, causing deaths and widespread damage.

Several regions, including areas north of the capital Lisbon, were affected by flooding and storms, prompting both candidates to adjust their campaigns to visit impacted communities and criticize the government's response.

Concerns over voter turnout have also emerged, as voting is not compulsory in Portugal. A new cold front bringing additional storms over the weekend raised fears of higher abstention, potentially affecting projections.

Ventura called for a postponement of the vote due to the weather conditions, but the government rejected the request.

One issue at stake is immigration, with Ventura deriding the influx of foreign-born individuals into the country over the past five years.

Polling stations across the country opened on Sunday morning at 8:00 a.m. (0800 GMT) and will close at 7:00 pm (1900 GMT) local time, with authorities urging voters to participate despite the adverse weather. Official results are expected later in the evening.