A bruising presidential campaign is drawing to a close in the Philippines with a last-minute attempt by the president to unify candidates against a front-running mayor perceived as a threat to democracy virtually collapsing.

After crisscrossing the archipelago nation for three months, five presidential candidates led by Mayor Rodrigo Duterte will converge in the vote-rich capital Saturday for their final rallies ahead of Monday's vote. Thousands of police have been deployed to maintain order.

On the eve of the end of campaigning, President Benigno Aquino III made a desperate call on candidates to agree to an alliance to defeat the brash Duterte, who has been likened to U.S. Republican front-runner Donald Trump for his controversial remarks but has topped pre-poll surveys on a pledge to wipe out criminals and corruption.