Duterte 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.
The raids from Monday to Tuesday resulted in the single largest death toll in one night of police operations since officers killed 16 people, including a city mayor, in a raid on a southern city on July 30.
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Police records from Bulacan province, a light-industrial centre just north of Manila, said that 26 anti-drug operations were conducted in 12 towns and cities, resulting in the killing of 21 "drug personalities".
The raids also resulted in the arrest of 64 suspects, the seizure of 21 firearms and about 100 grams of methamphetamines, popularly known as 'shabu' the records said.
A breakdown of the incidents showed that the 21 were killed in 16 separate operations where all the fatalities were armed, the police added.
Spokesperson for the Bulacan police could not be contacted for comment. Bulacan, a province of about 3.29 million people, has recorded numerous arrests and killings of drug suspects in recent months, the police records showed.
Duterte has vowed to protect police who kill drug suspects under suspicious circumstances. Government figures show that since Duterte took office last year up to July 26, a total of 3,451 "drug personalities" have been killed in police operations.
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More than 2,000 other people have been killed in drug-related crimes and thousands more murdered in unexplained circumstances, according to police data.
Despite warnings by human rights groups that Duterte may be overseeing a crime against humanity, he remains widely popular in the Philippines.
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