Police in the southern Philippines said they fatally shot a city mayor who was among the politicians President Rodrigo Duterte publicly linked to illegal drugs and at least 13 others Sunday (30 July), in one of the bloodiest assaults so far under Duterte's anti-drug crackdown.

Officers were to serve warrants to Mayor Reynaldo Parojinog Sr. of Ozamiz city to search his houses for the suspected presence of unlicensed firearms when gunmen opened fire on the police, sparking clashes that killed the mayor and at least 13 other people, police Senior Superintendent Jaysen de Guzman said by phone.

Aside from the mayor's residence, three other houses were raided in the port city in Misamis Occidental province and resulted in the arrests of five suspects, including the mayor's daughter. At least one police officer was wounded during the clashes, police said.

"We have reports that armed bodyguards are carrying unlicensed weapons," regional police Chief Superintendent Timoteo Pacleb said, adding that an undetermined number of assault rifles, grenades, suspected methamphetamine and cash were seized in the raids.

"The administration vowed to intensify the drug campaign," presidential spokesman Ernesto Abella said in connection with the police raids in Ozamiz. "The Parojinogs, if you would recall, are included in [Duterte's] list of personalities involved in the illegal drug trade."

Parojinog, who also faced corruption charges, had denied any links to illegal drugs. He was the third mayor to be killed under Duterte's bloody crackdown on drugs, which has left more than 3,000 dead in reported gunfights with police and thousands of other unexplained deaths of suspects.

The police officers were "met with volleys of fire from [the mayor's] security, prompting the Philippine National Police personnel to retaliate," Pacleb said. Parojinog, his wife and a brother were among the dead, police said.

Parojinog's daughter, Vice Mayor Nova Echaves, was arrested and was to be flown to Manila for security reasons, Pacleb said.

The drug killings have been widely criticised by Western governments and human rights groups that have called for an end to what they suspect were extrajudicial killings related to the anti-drug campaign.

Last year, police officers shot dead Albuera Mayor Rolando Espinosa Sr. inside a jail cell in the central province of Leyte, and a week before that, another mayor and his nine bodyguards were gunned down allegedly during a firefight on a road in the southern Philippines. Duterte has vowed to defend policemen, who would face criminal and human rights charges while cracking down on illegal drugs. He recently ordered a police officer charged in connection with Espinosa's death to be reinstated after briefly being suspended following the jail killing.

All three mayors were among more than 160 officials Duterte named publicly as being linked to illegal drugs in August last year as part of a shame campaign.

Duterte has vowed not to stop until the last drug trafficker in the country has been eliminated.