New Zealand Prime Minister Jacinda Ardern will tell the Philippines' President, Rodrigo Duterte, there have been too many killings in his war on drugs.

The Philippine government estimates at least 3000 people have been killed in the war on drugs, but human rights groups say more than 13,000 people are dead.

Mr Duterte's extra-judicial killings are popular locally, with 7 to 8 out of 10 Filipinos backing the war on drugs, but the policy has been widely condemned internationally.

Addressing media gathered in the Philippines for an ASEAN leaders' conference, Ms Ardern said the number of deaths "certainly requires investigations and oversight at the very least."

She said there have been various attempts at establishing oversight of the executions.

When asked whether she would say to Mr Duterte 'There have been too many killings'? Ms Ardern gave a definitive "yes."

During a speech in Vietnam on Friday, Mr Duterte boasted of murdering a man as a teenager. It's his latest claim of murder, having previously said he pushed a kidnapper out of a helicopter.

It wasn't the only international human rights issue Ms Ardern was questioned about.

When asked whether the situation for Rohingya Muslims in Rakhine State, Myanmar amounts to genocide, Ms Ardern wouldn't use that word but did say she was concerned.

"It's an intensely complex situation. I think it's absolutely fair that the international community raised concerns over what they've seen and the plight of those now refugees.

"Myanmar, though, is constantly probably aware of the civil conflict they've had in the past, and the role of the military is obviously still strong, but I join with others over their concern over what's happened in that state."

Meanwhile, Ms Ardern continues to extend New Zealand's offer to Australia to resettle refugees from Manus Island.

Newshub.