Japan and the United States are discussing ways to boost military cooperation, Tokyo's top government spokesman said Monday, after reports said US operations in the country could be strengthened to counter China.

Japanese media and the Financial Times, citing diplomatic sources, said a review of the allies' security pact will be announced at a US-Japan summit next month in Washington.

The reports said the move is part of steps to counter China's expanding military and political influence in the Asia-Pacific region.

"Japan and the United States have been discussing ways to strengthen cooperation in command and control in order to enhance interoperability and readiness," government spokesman Yoshimasa Hayashi told reporters.

"My understanding is that nothing has been decided regarding the American side's structure, including strengthening the functions of US Forces Japan," he said.

There are 54,000 US military personnel based in key US ally Japan.

Japan is ramping up defence spending to the NATO standard of two percent of GDP by 2027, and has warned that China poses the "greatest strategic challenge" to its security.

Japan's Yomiuri daily, citing US and and Japanese sources, reported Monday about the potential changes.

A permanent US-Japan joint team could be set up in Japan to ensure closer military coordination, the newspaper said, explaining that currently Japan has to deal with the Hawaii-based US Indo-Pacific Command for various decisions.

The Financial Times said that "the Pentagon is some way from making any decision", but that both Japan and the United States were keen to boost ties "to respond to what they view as a growing threat from China".

It also described the plans as "the biggest upgrade to (the US-Japan) security alliance since they signed a mutual defence treaty in 1960."

Prime Minister Fumio Kishida will meet US President Joe Biden on a state visit to Washington on 10 April.

Kishida is also due to take part in Japan's first three-way summit with the United States and the Philippines the following day.