Two Japanese tourists in their 20s were detained for two weeks in China then deported for taking photos showing exposed buttocks at the Great Wall, local media reported.

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 on 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.

The Japanese embassy 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.

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

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

A hashtag translating to "Japanese man and woman detained for indecent behaviour at the Great Wall" had been viewed more than 60 million times on 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 actor Chen Yitian, who has over seven million followers on the platform, condemned them for doing "shameful things on my Great Wall."

Others suggested China ban all Japanese visitors. (AFP)