Prime Minister Jacinda Ardern and Foreign Minister Winston Peters have congratulated Boris Johnson, the incoming British Prime Minister.

And they say Johnson's affection for New Zealand will help negotiations for a free trade agreement with the UK, a view shared by National leader Simon Bridges.

Johnson, the former mayor of London, swept to a convincing victory overnight, winning 66 per cent of the Conservative Party members' votes to defeat Jeremy Hunt.

But with a wafer-thin majority in the House of Commons, he still faces a huge challenge to see Brexit through.

Ardern congratulated Johnson via text message this morning.

"He said he was looking forward to working together," Ardern said.

"Mr Johnson is familiar with New Zealand in his former role as Foreign Secretary and has an excellent relationship with our Foreign Minister that I am sure will be mutually beneficial for our countries."

She said irrespective of the Brexit outcome, New Zealand will be ready to start FTA talks as soon as the UK was in a position to do so.

"I am sure that is something that Mr Johnson will want to discuss."

She said she would make a formal call to him once he had settled into his new role, and looked forward to meeting him at the UN General Assembly in September, where she would look to advance trade talks.

Peters told Radio NZ this morning that Johnson was a "seriously intelligent chap" with a lot of affection for New Zealand.

"When he stood down in as Foreign Secretary last July, I sent him a text saying he would be back. And last night, he was back.

"Boris Johnson does have that sense of respect and affection ... We will hit the ground running in far better shape."

Johnson favours a "hard Brexit", whereby the UK would be completely cut out of the EU and taking it out of the single market but would have more control over its borders.

Peters shares this view.

"The sooner [British MPs] face the facts that it will be a hard landing and prepare for that and get on with the future, the better," he said in January.

Peters calls Johnson a friend and told a select committee last month that he would become Prime Minister.

"He's going to be the Prime Minister, and he's going to be an excellent Prime Minister. He's got what the ordinary British people want – character and courage," Peters told the Foreign Affairs and Trade select committee.

Last year Peters and Johnson met in the Churchill War Rooms in London to discuss the UK's plan to scale up its engagement in the Pacific.

In mid-2017, Johnson came to New Zealand and said New Zealand and the UK have a strong relationship.

National Party leader Simon Bridges, who was Transport Minister when he met Johnson in 2017, welcomed Johnson's victory.

"What impressed me is we had a detailed discussion on infrastructure funding and he clearly got it," Bridges said.

"He will be good for New Zealand. He believes in being closer with the Commonwealth and his position on Brexit makes a stronger Free Trade Agreement with us much more likely.

"As he himself has said, we will be at or near the front of the queue."