Filipinos will vote in a mid-term election seen as a referendum on the feud between President Ferdinand Marcos (pictured) and impeached Vice President Sara Duterte
Filipinos will vote in a mid-term election seen as a referendum on the feud between President Ferdinand Marcos (pictured) and impeached Vice President Sara Duterte AFP

Millions of Filipinos will vote Monday in a mid-term election widely seen as a referendum on the explosive feud between President Ferdinand Marcos and impeached Vice President Sara Duterte.

Workers in the capital Manila were busily setting up polling stations Sunday for a race that will decide more than 18,000 posts, from seats in the House of Representatives to hotly contested municipal offices.

It is the Senate race, however, that carries potentially major implications for 2028's presidential election.

The 12 senators chosen Monday will form half the jury in a Duterte impeachment trial -- tentatively set for July -- that could see her permanently barred from public office.

Duterte's long-simmering feud with former ally Marcos exploded in February when she was impeached by the House for alleged "high crimes" including corruption and an assassination plot against the president.

Barely a month later, her father, former president Rodrigo Duterte, was arrested and flown to the International Criminal Court (ICC) the same day to face a charge of crimes against humanity over his deadly anti-drugs campaign.

Sara Duterte will need nine votes in the 24-seat Senate to preserve any hope of a future presidential run.

Heading into Monday, seven of the candidates polling in the top 12 were endorsed by Marcos while four were aligned with his vice president.

Two, including the president's independent-minded sister Imee Marcos, were "adopted" as honorary members of the Duterte family's PDP-Laban party on Saturday.

The move to add Marcos and television personality Camille Villar to the party's slate was intended to add "more allies to protect the Vice President against impeachment", according to the resolution.

At her final rally in Manila on Thursday, Duterte invoked the spectre of "massive" electoral fraud and once again referred to her father's transfer to the ICC as a "kidnapping".

Despite his detention at The Hague, the elder Duterte remains on the ballot in his family's southern stronghold of Davao city, where he is seeking to retake his former job as mayor.

At least one local poll is predicting he will win comfortably.

National police in the archipelago nation have been on alert for more than a week, and around 163,000 officers have been deployed to secure polling stations, escort election officials and guard checkpoints.

Thousands more personnel from the military, fire departments and other agencies have been mobilised to keep the peace in a country where battles over hotly contested provincial posts are known to erupt in violence.

A city council hopeful, a polling officer and a village chief are among the at least 16 people police say have been killed in attacks in the run-up to Monday's election.

On Saturday, a candidate for municipal councillor was one of two men in an "armed group" killed in a shootout with police and the military in southern Mindanao island's autonomous Muslim region, a notorious hotbed of election-related violence.

Further north, a group of men were arrested the same day at the Cebu airport while transporting 441 million pesos (nearly $8 million) in cash, a crime under election rules aimed at preventing the exchange of bribes for votes.

Both cases were still under investigation.

Impeached Vice President Sara Duterte will need nine votes in the 24-seat Senate to preserve any hope of a future presidential run
Impeached Vice President Sara Duterte will need nine votes in the 24-seat Senate to preserve any hope of a future presidential run AFP