A strike group of Royal Navy ships spearheaded by the giant new aircraft carrier HMS Queen Elizabeth is en route to the Asia-Pacific region.

After exercises with allied navies, it will pay visits to five Japanese ports in September, officials said during a visit by Defence Secretary Ben Wallace to Tokyo.

In addition, the offshore patrol vessels HMS Spey and HMS Tamar will start a permanent deployment to the region next month, supported by ships from Australia, Japan and Singapore.

China claims sovereignty over most of the South China Sea, angering its regional neighbours and triggering protests further afield including from the US government.

Wallace said Britain had a "duty" to insist on freedom of navigation when the carrier strike group sails through the sea on its way to Japan.

"It's no secret that China shadows and challenges ships transiting international waters on very legitimate routes," he told The Times newspaper in Tokyo.

"We will respect China and we hope that China respects us," he said, stressing: "We will sail where international law allows."

Last month, Russia issued strong protests at what it said was a British destroyer's violation of its territory in the Black Sea.

The UK, which does not recognise Russia's annexation of the Crimea, insisted HMS Defender was in legitimate waters off Ukraine. The ship has since joined the rest of the carrier group.

For all its bristling power, the Royal Navy deployment is not immune to Covid-19. More than 100 of HMS Queen Elizabeth's 1,600 crew were struck down during a port call in Cyprus earlier this month.

Wallace said the ships will observe strict Covid protocols in Japan, and underlined at a news conference the two nations' shared commitment "to protect rules-based international order".

Japanese Defence Minister Nobuo Kishi echoed Wallace after the two held talks.

"We reconfirmed our shared position that we firmly oppose attempts to change the status quo by coercion, and the importance of a free and open Indo-Pacific based on rule of law," he said.