Philippine President Rodrigo Duterte has repeated threats to kill municipal mayors involved in drugs as the number of Filipinos killed in his deadly crackdown tops 6200.

"I might go down in history as the butcher. It's up to you," Mr Duterte told 1635 town and city mayors he summoned to the presidential palace.

"I will ask the chief of police to shoot you," he said.

Antonio Halili, the mayor of Tanauan City, near Manila, said that during the meeting Mr Duterte fumed about drugs destroying "the moral fabric of society".