Former Prime Minister Sir John Key says New Zealand's relationship with China is critical and needs to be treated accordingly. 

Jacinda Ardern has just finished a whirlwind trip to China, where she met with President Xi Jinping and the Premier  Li Keqiang, to discuss our diplomatic relationship, human rights and Huawei. 

John Key told Mike Hosking our relationship with China is incredibly important and a critical part of our economy.

"That's why as Prime Minister I went there seven times, a huge number of our ministers went there and over time every member of the political bureau came to New Zealand."

However, he said the Prime Minister's visit to China shows they are invested in the relationship.

"It's a good sign that Jacinda had the invitation to go out there...that matters in their culture (face time), so let's see how things progress."

He said the briefness of the trip shouldn't have been an issue given the circumstances.

"The reality is that those trips are based around a one day basic where you see the Premier and the President. The rest of the time you typically take a trade delegation, leverage what we are doing up there and have the opportunity to promote KJiwi companies."

Key said China follows New Zealand closely and the government needs to think carefully about what they say and do. 

"When we say something they take us seriously. So all I can say is, as a country and a government, the government has to take its comments really carefully and monitor them."

He said whether we like it or not, China plays a huge part in New Zealand's trade and therefore is a critical partner for us. 

"Take a look at Europe, I started trying to do a Free Trade Agreement with Europe years and years ago, the FTA isn't over the line yet, maybe it will be but no one should expect anything other than huge resistance from French farmers."

"You look at the United States, well yep, we had an FTA going with TPP well, Trump has pulled out of that."

"China is the only country effectively where have unfettered access to all parts...If we treat that relationship properly we will continue to prosper off the back of that."

The Former Prime Minister said people don't need to be concerned by China's involvement in New Zealand.

He said people are becoming increasingly concerned about things like the belt and road project.

Commissioned by the New Zealand China Council, Belt and Road Initiative is pitched as a first step toward a strategic plan to maximise the benefits of Beijing's massive global infrastructure push.

The Belt and Road Initiative (BRI) was announced in 2013 by President Xi Jinping, who described it as the project of the century.

It seeks to enhance economic growth across the traditional Chinese trade routes – over land to Europe and by sea down through the Pacific.

Sir John Key said the initiative isn't something to be worried about because China has always been involved in New Zealand.

"As a country emerges as a superpower, and let's be frank, China is going going to go past the United States as a nominally larger economy very soon and over time its GDP per capita...is growing dramatically. So if they get anywhere near the United States in the next 50 years, they will have the better part of a billion consumers (three times the United States) spending enormous amounts of money and buying products."

He said our relationship with China needs to be treated really carefully.