Twelve people, including a city mayor, were killed on Sunday in a shootout with police officers during a series of pre-dawn anti-drug raids in the southern Philippines, police and local officials said.

Police officers also arrested the vice mayor of Ozamiz City, about 780 kilometers south of Manila, during the raids, said Chief Superintendent Timoteo Pacleb, a regional police director.

Police simultaneously served search warrants against the properties of Reynaldo Parojinog Senior, mayor of Ozamiz City, his daughter Vice Mayor Nova Parojinog and three other family members on allegations they were trading in illegal drugs, Pacleb said.

"The police personnel were met with a volley of gunfire from their security, prompting the police to retaliate," he added.

Aside from Parojinog, his wife, a provincial board member who was also a relative and four security aides of the family were among those killed in the shoot-out, Pacleb said.

The identities of the other people slain were still being verified.

Police confiscated high-powered firearms and an undetermined amount of methamphetamine hydrochloride, locally known as shabu, from at least four houses of the Parojinog family, the city's information office said.

Last week, Philippine President Rodrigo Duterte vowed that his aggressive campaign against illegal drugs will not ease despite mounting criticism over the rising death toll.

More than 3,000 suspects have been killed in anti-drug operations since Duterte became president on June 30, 2016, according to police statistics. But human rights groups have warned that the actual death toll could be higher.