Deputy Prime Minister Grant Robertson says the new British leader is a "good friend of New Zealand" and revealed they'd worked closely together during Covid-19.
At the same time as heaping praise on Rishi Sunak however, Robertson deferred when asked about Chinese President Xi Jinping gaining a historic third five-year term, saying he wouldn't comment on an "individual political party's processes".
His comments continue a cautious approach to diplomacy with New Zealand's biggest trading partner, where there are also major concerns about human rights abuses.
Sunak has become Britain's third PM in two months, taking over from Liz Truss, who will officially step down early on Wednesday.
Sunak, of Indian heritage and the nation's first non-white leader, was previously Chancellor of the Exchequer (finance minister in New Zealand) under Boris Johnson and impressed through the pandemic.
Robertson, who is also Finance Minister, said he had got to know Sunak over that period - "mostly online".
"Rishi is a good friend of New Zealand. During the Covid period, I had a number of conversations with him.
"We talked a lot about the responses our countries were taking.
"He is a supporter of the free trade agreement, which is great as it finds its way through the British Parliament.
"And I think he'll be a person New Zealand can work well with the build on what's already a strong relationship."
Robertson said he would be facing "very significant economic issues" in the UK at the moment.
"As he said himself, inflation is up over 10 per cent, the energy crisis, the war in Ukraine, so it's going to be a very tough time for him."
National Party leader Christopher Luxon was equally lavish in his praise, calling him a "good champion of New Zealand" in supporting the free trade agreement.
Luxon said he faced a "very tough set of circumstances" economically, not "dissimilar" to challenges here.
Over the weekend the Chinese leader was also announced, with Xi reaffirmed Communist Party leader and given a historic third five-year term.
At the same time, the party congress removed Premier Li Keqiang from senior leadership. Li, the nation's No 2 official, is a proponent of market-oriented reforms, which are in contrast to Xi's moves to expand state control over the economy.
Asked about Xi's reappointment, Robertson said he was "not going to comment around individual political party's processes".
He said New Zealand's relationship with China was "an important one" and would continue to be so.
"Those decisions that were made at the party congress are ones that the Chinese Communist Party has made."
National Party foreign affairs spokesman Gerry Brownlee said New Zealand had a "respectful relationship with China" and this would not change despite Xi further entrenching his rule.
"President Xi is very aware of New Zealand and what we stand for.
"We will continue to speak with Chinese counterparts the way we always have, making clear that while we appreciate the trading relationship, we have some significant differences when it comes to human rights."
National MP Simon O'Connor, who co-chairs the Inter-Parliamentary Alliance on China, said he felt the relationship would continue strongly because trade was important.
"But let's also be clear that he's an autocratic ruler over a communist state, and he's entrenching his power further."
O'Connor said there were concerns about human rights issues and conflict with Taiwan.
"I think it'd be hard to backslide much further on human rights abuses, particularly the likes of the Uighurs.
"I think we need to be very concerned about the Taiwan question. Xi has been very clear in his speeches that he intends to take it back and is not taking military options off the table.
"That should be of concern to all New Zealanders."