Philippine presidential candidate Rodrigo Duterte Saturday renewed his vow to kill criminals as the tough-talking favourite hit the stump in the capital heading into the home stretch of a controversial campaign.

Seen by fans and foes alike as a real-life "Dirty Harry" from a southern city made infamous by shadowy vigilante death squads, the 71-year-old mayor of Davao is the surprise favourite in the race to succeed President Benigno Aquino.

"The drug pushers, kidnappers, robbers, find them all and arrest them. If they resist, kill them all," he told about 2,000 people who cheered and shook their fists during a central Manila rally shortly after midnight.

"Go ahead and charge me with murder, so I could also kill you."

Duterte had earlier pledged to kill 100,000 criminals and dump so many in Manila Bay that the "fish will grow fat" from feeding on them.

Analysts say Duterte's profanity-laced campaign resonates in a chaotic, high-crime society with limited opportunities for a vast underclass working for a tiny elite.

His April 12 comments, in which he suggested that as mayor he should have been the first in line to rape the victim, drew widespread public condemnation, including from the ambassadors of key allies the United States and Australia.

The unrepentant candidate later told the envoys to "shut up" and steer clear of domestic politics, while also grudgingly issuing an apology over the rape comments.

He has also vowed to hold direct talks with China to resolve overlapping claims in the South China Sea, in a reversal of Aquino's policy of multilateral discussions with other claimants and international arbitration.