"Let us not be naive about China," Secretary General Mark Rutte told the Japan Times.

"The build-up of their armed forces and investments in their defence industry, and in their defence capabilities, is staggering," Rutte said in the interview published on Monday.

The comment came as he visited the Yokosuka naval base and a Japanese defence contractor on Tuesday before meeting defence minister Gen Nakatani to call for further cooperation.

"NATO and Japan share the same values and we face many of the same challenges," Rutte told Nakatani.

"China, North Korea and Russia are stepping up their military exercises and their cooperation, undermining global stability, and that means what happens in the Euro-Atlantic matters for the Indo-Pacific and vice versa.

"A stronger Japan-NATO cooperation is necessary in an increasingly dangerous world," he said.

Nakatani echoed the sentiment as Japan goes through a multi-year project to double its military spending to meet changing threats.

Rutte was due to meet Prime Minister Shigeru Ishiba on Wednesday.

The visit came as US President Donald Trump pressures other members of the mainly European NATO alliance to increase their military spending.

At the same time Trump wants Asia-Pacific allies to beef up their militaries to help confront China and contain North Korea.

"The US wants NATO to be more involved (in the region). Not in an Article 5 sense, but in a sense of projecting power, having each other's back within NATO," Rutte said in the Japan Times interview.

NATO's Article 5 provides that if a member nation is attacked, all others will consider this an attack on all and will take action accordingly.

NATO has moved to boost ties with Japan, South Korea, Australia and New Zealand -- the so-called IP4 -- in recent years, with their leaders attending NATO summits.

Rutte told the Japan Times last week that NATO wanted to take this partnership to the next level by stepping up information-sharing and defence-industrial cooperation.

"We have to move beyond... joint declarations... let's make it practical," said the Dutchman, who became NATO chief last October.

Japan has increased military cooperation with countries in Europe and last November Tokyo and the European Union announced a new security and defence partnership.