"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.

US President Donald Trump is pressuring 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.

"More and more 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.

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.

Rutte was due to visit the Yokosuka naval base on Tuesday and meet senior Japanese officials including, on Wednesday, Prime Minister Shigeru Ishiba.

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.