Prime Minister Jacinda Ardern sends warning to China alongside Japanese counterpart Fumio Kishida

On her last day in Tokyo, Prime Minister Jacinda Ardern says an information-sharing deal will include top secret information, and alongside her Japanese counterpart has sent China a warning.

Ardern was given a grand welcome in Japan with a guard's honour. There were handshakes and photographs, before things got serious. 

"Today I had a frank discussion with Prime Minister Ardern resulting in concrete outcomes on how to strengthen partnership," Japanese Prime Minister Fumio Kishida said at a press conference. 

The talks were frank and fruitful, with the finalisation of a spy deal months in the making. 

"This will support closer engagement in support of peace, stability and security in the Pacific and in the wider Indo-Pacific region," Ardern said. 

The Prime Minister says the deal will mean we can formally share what intel we have in situations like the Tongan volcano eruption. But it's also much, much more than that.

"Up to the level of top secret, and at our discretion," Ardern told reporters, when asked about the scope of the agreement. "As I say, at the moment [we're] still in the process of negotiating the scope of the arrangement."

Though there are no plans to add a sixth eye to the Five Eyes spy pact.

"I'm cautious about what I discuss in terms of intelligence-sharing arrangements and the nature of five eyes."

The leaders made a point of being united against the militarisation of the Indo-Pacific - a shot across China's bow.

The superpower recently flew fighter jets over the South and East China Seas and signed its controversial Solomon Islands security pact.

"Attempts to unilaterally change the status quo by force cannot be allowed in any region, wherever that may be," said Prime Minister Kishida. 

Ardern said any threat to another nation's sovereignty will not be tolerated.

"It is about demonstrating through global action that there will be a swift response should that occur in any other region or country."

The other goal of the visit was to get more international students to come to New Zealand. But universities who depend on international students for fees are battling to actually get them in. Pre-pandemic, 80,000 came in.

"Our biggest challenge is basically making sure students can get through Immigration New Zealand's visa processing," said Chris Whelan, executive director of Universities New Zealand. 

"Right now we have 5000 students able to come through this year, which is as much as Immigration New Zealand can process."

Ardern said: "It's really important that at this juncture, as our borders are reopening and as our international education programme scales up again, that we're back in the market promoting international education."

Though there's no promise to sort out immigration issues.