The incident at the World Heritage site near Beijing concerned a man who showed his bottom and a woman who took photos, NTV and other Japanese media outlets reported on Thursday.

Tokyo's foreign ministry said Friday that "the Embassy of Japan in China confirmed on January 3 that two Japanese nationals were detained by local authorities at the Great Wall."

They "were subsequently released and returned to Japan during January", it said in a statement.

The Japanese embassy in Beijing did not reply to requests for comment.

The tourists were detained on the spot by security guards and held for around two weeks, the reports said, citing sources.

Exposing the lower half of the body in a public place is against the law in China, according to the reports.

The tourists reportedly told the Japanese embassy they did it as a prank.

The reports sparked outrage in China, where memories of atrocities committed during Japan's colonial occupation of the country in the 1930s and 40s still inspire strong feelings.

A hashtag translating to "Japanese man and woman detained for indecent behaviour at the Great Wall" had been viewed over 60 million times on social media platform Weibo by Friday morning.

Many top-liked comments blasted the tourists for the act, with some using hateful language toward Japanese people.

One comment by Chinese actor Chen Yitian, who has over 7 million followers on the platform, condemned them for doing "shameful things on my Great Wall".

Others suggested China ban all Japanese visitors.