Singaporeans head to the polls Friday in the city-state's first contested presidential election in more than a decade, a vote being closely watched as an indication of support for the ruling party after a rare spate of political scandals.

The president's role is largely ceremonial, but there are stringent requirements for the position, which formally oversees the city's accumulated financial reserves and holds the power to veto certain measures and approve anti-graft probes.

While the presidency is a non-partisan post under the constitution, political lines were already drawn ahead of the election to replace incumbent Halimah Yacob, who ran unopposed for her six-year term in 2017.

The city-state's government is run by the prime minister, currently Lee Hsien Loong of the People's Action Party, which has ruled Singapore continuously since 1959.

Observers said the vote could indicate the level of PAP support ahead of general elections due by 2025 or discontent after recent scandals that include a corruption probe into the transport minister and the resignations of two PAP legislators over an affair.

The frontrunner is former deputy prime minister and finance minister Tharman Shanmugaratnam, a long-time PAP stalwart before he resigned ahead of his candidacy.

The 66-year-old economist is widely perceived as having the government's backing and was questioned about his independence during the campaign.

Another candidate, former insurance executive Tan Kin Lian, 75, has gained the support of several opposition leaders.

The third candidate, Ng Kok Song, 75, is the former chief investment officer of Singapore sovereign wealth fund GIC, which manages the country's foreign reserves.

"The presidential election is increasingly being treated as a general election," said Mustafa Izzuddin, a political analyst with consultancy Solaris Strategies Singapore.

"An increase in protest voting is anticipated due to vacillating ground sentiments vis-a-vis the ruling government."

The PAP was recently rocked by political scandals, a rarity in the city which has capitalized on its reputation for clean government to become an international hub for an array of industries like finance and aviation.

The PAP suffered its worst-ever election performance in 2020 but maintained its more than two-thirds majority.

Voting is compulsory for Singapore's more than 2.7 million eligible citizens. Those who do not vote without a valid reason risk being struck from the voters' list.

Singapore requires presidential candidates to have served either as a senior civil servant or the chief executive of a company with shareholder equity of at least 500 million Singaporean dollars ($370 million).

Perhaps the president's most crucial function is to serve as a custodian of Singapore's financial reserves, which can only be drawn upon in exceptional circumstances, such as the COVID-19 pandemic and the 2009 global financial crisis.