Police shot dead six supporters of a Philippine mayor Wednesday, authorities said, days after President Rodrigo Duterte threatened to have him "shot on sight" for protecting his drug-dealing son.

Hundreds of people have died since Duterte took power after winning a landslide election on the pledge to wipe out lawlessness by killing tens of thousands of criminals.

A gunfight broke out between law enforcement and supporters of mayor Rolando Espinosa at dawn on Wednesday in his central hometown of Albuera, local police said.

Six gunmen were killed while police recovered 17 guns and several grenades, they said.

On Monday, Duterte gave the mayor and his son 24 hours to surrender after two of the mayor's bodyguards and three other employees were arrested in a police anti-drug operation.

"Otherwise, an order of 'shoot on sight' will be given if they resist and endanger the lives of arresting police officers," presidential spokesman Ernesto Abella said on television.

Espinosa surrendered to police on Tuesday, saying he feared for his safety after the president threatened reprisals for allegedly coddling his drug-dealing son.

The mayor "surrendered to me... (following) orders of the president for him to be shot on sight if he resists," national police chief Ronald de la Rosa said.

Police claim to have killed more than 400 suspected drug dealers since Duterte was elected, but rights groups fear the total could be far higher as vigilantes have joined the spree.

The rising body count has shocked the world, and hundreds of anti-narcotics and human rights groups on Tuesday called for the UN to condemn Duterte's policy.

De la Rosa said Espinosa had been listed in police records as a "drug protector" whose son controlled the narcotics trade in the Albuera region.

"If you're listening now Kerwin, your father has already surrendered so you should follow your father," de la Rosa said in a bizarre, live news conference with Espinosa.

"If you don't surrender you will die so better surrender because your life is really in danger."

The mayor was the second high-profile drug suspect to turn himself in after being accused of drugs-related crimes by Duterte.

Last month, in a meeting also aired on national television, the president told a businessman he would "finish you off" unless he stopped dealing in drugs. The businessman denied the allegations.

Police said more than 100,000 other people have also surrendered to the local authorities and pledged to stop using illegal drugs.