WELLINGTON -- New Zealand's relationship with China is growing in importance and strength as the two countries expand cooperation and exchanges, New Zealand Prime Minister John Key said ahead of his visit to China starts later this week.

In an exclusive interview with Xinhua, Key said he anticipated that he and any successive New Zealand leaders would likely make an annual visit to China to continue strengthening bonds between the two nations.

"We've been to China pretty much every year I've been in office other than election year and that's a reflection of how seriously we take the relationship and how important we think the relationship is," Key said at Parliament Building in Wellington.

"I think that will continue. I'm convinced that in the entire time I'm prime minister I'll be fairly confident I'll be in China every year. I'm sure whoever takes over from me one day when I'm no longer prime minister will continue to do that because that's the significance of the relationship," he said.

"From our point of view we treasure the relationship with China because we think it's a very important one and we think it'll be a very significant one."

Key will lead one of the country's largest ever prime ministerial delegations abroad on his third trip to China since becoming prime minister in 2008.

His visit to China would be "symbolic" to mark the 40th anniversary of bilateral diplomatic ties and the fifth anniversary of the free trade agreement (FTA) with China, but would also be an opportunity to meet President Xi Jinping and Premier Li Keqiang in their new capacities in China's new leadership.

"We have a big trading relationship with China and now they're our largest source of foreign students; they're our second largest source of tourists; they're our second largest market overall," said Key.

"We're seeing a big change in our trading patterns. There's also a growing investment in both our markets happening, with China increasingly investing in New Zealand and New Zealand companies investing in China. So from a trade and economic perspective there's a lot happening in the relationship."

New Zealand was also very pleased to be the only developed economy to have a FTA with China, giving it an advantage in the Chinese market.

"I think it's worked for China and I think it works for New Zealand," he said.

The two countries were also working together in the field of development and aid, as seen in the joint project to build a water reticulation plant in the Cook Islands, as well as exchanging ideas and views in areas including climate change and science.

"So at so many different levels we have a multi-faceted relationship with China and it's one that continues to grow in importance and strength," said Key.

China's remarkable economic performance had helped lift the global economy and mitigate the adverse effects of the global financial crisis, and its international importance would continue to grow, Key went on to say.

"Clearly this is an important point in the development of China and so New Zealand wants to have an opportunity to present ourselves and to talk about the relationship and how we can continue to grow from strength to strength," he said.

New Zealand exports to China have more than tripled since the signing of the FTA to 6.9 billion NZ dollars ($5.8 billion) last year, up 16.6 percent on the previous year, and last year nearly 200,000 Chinese visitors came to New Zealand, up 35 percent on the previous year.

The seven-day visit, which starts from April 6, will include a meeting with President Xi at the annual Bo'ao Forum for Asia conference on April 7.

Key will also be officially welcomed by Premier Li at Beijing's Great Hall of the People and visit the cities of Guangzhou and Shanghai.