Prime Minister Sanae Takaichi did not visit in person the Yasukuni Shrine in central Tokyo, which is dedicated to 2.5 million war dead, mostly Japanese, who perished in conflicts since the late 19th century.

That number includes senior military and political figures convicted by an international tribunal of war crimes prior to and during World War II.

China reacted angrily to the offering, calling the shrine a "spiritual instrument and symbol of the wars of aggression launched by Japanese militarism."

"China firmly opposes and strongly condemns the negative moves by Japan regarding the Yasukuni Shrine, and has made solemn representations and a strong protest to the Japanese side," foreign ministry spokesman Guo Jiakun said.

South Korea expressed "deep disappointment and regret".

"Our government urges Japan's responsible leaders to face history squarely and to demonstrate, through action, a humble reflection on and a sincere remorse for its past," foreign ministry spokesman Park Il told reporters.

- Visits to flashpoint memorial -

A Japanese prime minister has not visited the shrine since 2013, but Takaichi's predecessors Shigeru Ishiba and Fumio Kishida regularly sent offerings for the biannual spring and autumn festivals.

Dozens of lawmakers pay their respects every year during the festivals and in August for the anniversary of the emperor announcing Japan's surrender in 1945.

Former prime minister Shinzo Abe visited the shrine in 2013, sparking fury in Beijing and Seoul and earning a rare diplomatic rebuke from close ally the United States.

Takaichi sent a "masakaki" tree offering, an unidentified source close to the matter told AFP, while public broadcaster NHK and Jiji Press also reported that she sent the offering.

The conservative premier kept tightlipped when asked by reporters whether she would visit the shrine in person after offering the masakaki.

"Since it is a private matter, I have nothing to say about it here today," she told reporters at her Tokyo office.

"I believe that, regardless of the country, it is only natural to pay respect and express gratitude to those who gave their lives for their nation and to those who followed their country's policies," she said.

Takaichi visited the shrine in August last year, before she became prime minister, and told local media: "Honouring the spirits of those who devoted their lives for their country is something each individual should do in accordance with their own conscience."