Police killed at least 32 suspected drug offenders in a series of raids near Manila, in the bloodiest night of Philippine President Rodrigo Duterte's war on drugs.

Senior Superintendent Romeo M. Caramat Jr. said 67 operations in various parts of Bulacan province Tuesday saw police kill dozens, while 109 others were arrested.

Police also claimed to have seized more than 200 grams of methamphetamine, 786 grams of cannabis, assorted firearms, grenades and ammunition.

Bulacan, a province of about 3.29 million people, has recorded numerous arrests and killings of drug suspects in recent months, police records showed.

Duterte has vowed to protect police who kill drug suspects under suspicious circumstances.

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Government figures show that since Duterte took office last year up to July 26, more than 3,000 "drug personalities" have been killed in gun battles with police.

More than 2,000 others died in drug-related homicides, including attacks by motorcycle-riding masked gunmen and other assaults. Human rights groups report a higher toll.

Despite warnings by human rights groups that Duterte may be overseeing a crime against humanity, the leader remains widely popular in the Philippines.

He won a landslide victory in presidential elections last year after promising an unprecedented war on drugs in which tens of thousands of people would be killed.

Meanwhile in neighbouring Indonesia, Amnesty International said on Wednesday that police were taking a leaf out of Duterte's "war on drugs" and have killed 60 suspected drug dealers so far this year, compared to 18 in all of 2016.