The Philippine president has compared his bloody anti-drug campaign, which has left more than 3,000 people dead, to how Hitler massacred millions of Jews, saying he would be "happy to slaughter" 3 million addicts.

President Rodrigo Duterte issued his latest threat against drug dealers and users early Friday on arrival in southern Davao city after visiting Vietnam, where he discussed his anti-drug campaign with Vietnamese leaders among other concerns.

Duterte says: "Hitler massacred three million Jews ... there's three million drug addicts. There are. I'd be happy to slaughter them." Historians say that 6 million Jews were killed by the Nazis under Hitler before and during World War II.