Philippines President Rodrigo Duterte appears to have likened himself to Adolf Hitler, saying he would "be happy" to exterminate three million drug users and peddlers.

His comments angered Jewish groups in the United States, which could add to pressure on the US government to take a tougher line with the Philippines leader.

Duterte recently insulted President Barack Obama and in a number of remarks he has undermined the previously close relationship between Manila and Washington.

In a rambling speech on his arrival in Davao City after a visit to Vietnam, Duterte told reporters that he had been "portrayed to be a cousin of Hitler" by critics.

Noting that Hitler had murdered millions of Jews, Duterte said, "There are three million drug addicts [in the Philippines]. I'd be happy to slaughter them.

"If Germany had Hitler, the Philippines would have ...," he said, pausing and pointing to himself.

"You know my victims. I would like [them] to be all criminals to finish the problem of my country and save the next generation from perdition."

Duterte was voted to power in a May election on the back of a vow to end drugs and corruption in the country of 100 million people.

He took office on June 30 and over 3100 people have been killed since then, mostly alleged drug users and dealers, in police operations and vigilante killings.

The Anti-Defamation League, an international Jewish group based in the United States, said Duterte's comments were "shocking for their tone-deafness".

While the Obama administration has criticised Duterte over the extra-judicial killings, US officials offered no immediate condemnation of his latest comments and instead stuck to a strategy of stressing long-standing ties with Manila.

Two days before the Philippines election, outgoing President Benigno Aquino had warned that Duterte's rising popularity was akin to that of Hitler in the 1920s and 1930s.

"I hope we learn the lessons of history," Aquino said in widely reported remarks. "We should remember how Hitler came to power."