I'll express 'disagreement' with US on climate change - Bill English

Prime Minister Bill English says he will voice New Zealand's disapproval of the United States' decision to leave the Paris Climate Agreement in a meeting with US Secretary of State Rex Tillerson on Tuesday.

In an interview with The AM Show on Tuesday morning, Mr English said he will make clear New Zealand's "disagreement with their point of view" on climate change - but said it wouldn't be at the demise of the two countries' relationship.

The remarks come as hundreds of protesters prepare to demonstrate outside Parliament in opposition to the US' attitude to climate change.

Environmental organisation 350 Aotearoa says around 500 people are expected to show up to protest when Mr Tillerson arrives there at about 12:30pm.

Mr English says he accepts Mr Trump's decision as it's "just part of their domestic politics" - and he says there's plenty of other things to talk about with Mr Tillerson when they meet.

"There's other areas where we have tension and disagreement with the US but fundamentally, they underpin the economic and security stability of the Asia-Pacific - and that's important to New Zealand," Mr English told Duncan Garner.

One of the things that will be discussed, alongside talks on trade, terrorism and Antarctica, is whether New Zealand will send two more troops to Afghanistan.

"There's a formal request that's been made - we're considering that, and I don't think there'll be anything more than that required today," he said.

"I think the terror attacks in London show New Zealand has a role around the world in doing our part … if Afghanistan becomes some kind of place where terrorism can thrive then we want to play a role in stabilising Afghanistan."

Mr English has warned Kiwis travelling to London that there is a severe terror warning in place in the city, and says New Zealanders should consult the travel advisory before heading there if worried about potential threats.

Meanwhile Mr English has spoken about his decision to knight the man he once deputised for - but has kept tight-lipped on whether Sir John Key could have received a higher honour.

It was revealed on Monday that Mr Key had received a knighthood for services to the state - but Mr English refused to comment on whether he had offered the ex-Prime Minister an Order of New Zealand, our nation's highest honour.

"This is the appropriate honour at the time, and that's why he's now Sir John Key," he said. "I'm not going to go into the details of it all - but as you can see, John's very happy.

"It's a process where there's a committee involved, hundreds of people considered - Sir John Key was one of them. There's many others and there's a lot of diversity in the list that came out, and I'm very proud of all they've done for New Zealand."