The new rules permitting the sale of lethal weapons overseas signal a major shift, as Japan ramps up its defence ambitions and seeks to enter the global arms market in part to boost economic growth.

The move, announced this week on Tuesday by Prime Minister Sanae Takaichi's government, has been met with some criticism and unease among the Japanese public.

Holding placards that read "Stop exporting lethal weapons!" and "No war", dozens of protesters assembled on Friday in front of a busy train station in the capital's Shinjuku area, an AFP journalist said.

"The government must not decide on its own," they chanted.

Tokyo resident Ryozo Sawada told AFP he felt "an unbearable sense of humiliation" about the policy shift.

"Ever since I was a child, the one thing about Japan I could truly be proud of was that we renounced war," the 74-year-old said.

"The fact that they actually decided to export weapons is incredibly frightening," said Masako, a 29-year-old Tokyo resident who only gave her first name.

"I'm angry that, even though Japan has been a peaceful nation for the past 80 years, a small group of people did something that outright denies that," she said.

When announcing the change, Takaichi stressed that Japan's "core principles" and "history" as a pacifist nation remain unchanged.

- 'Never again' -

At the Shinjuku rally, 31-year-old writer Yura Suzuike expressed concern that "Japan might end up taking part in... the senseless violence happening around the world".

In World War II, "Japan committed acts of aggression, and in turn suffered enormous damage from the atomic bombs", Suzuike told AFP.

Japan's pacifist constitution that followed had been drafted "with the resolve that we must never again wage war or kill people", she said.

The change has provoked an angry reaction from China, whose escalating military activity in the region as well as persistent security threats from North Korea and Russia have increased anxiety in Japan.

Proponents argue the change, which was approved by the cabinet and the National Security Council on Tuesday, would further integrate Tokyo in the international defence supply chain, deepening ties with partner nations in the face of regional instability.

Exports had previously been limited to equipment classified under five categories: search and rescue, transportation, warning, surveillance and minesweeping.

Under the new rule, Japan could export weapons only to countries that pledge to use them in a manner consistent with the United Nations Charter.

A March survey by national broadcaster NHK suggested that around half of Japanese opposed the change, with 32 percent of respondents saying they support it.

Peace activists have staged rallies across the nation over concerns that Takaichi's hawkish views and open support for US President Donald Trump could drag Japan into conflicts.