In the latest public relations blow to Tokyo after plans for its $2 billion Olympic stadium were ditched, a Belgium-based designer took to social media to register surprise over the similarities between the logos.
"Striking when you know the Liege Theatre logo has been regularly shared on Pinterest," Studio Debie wrote on its Facebook page.
"Even the typography is the same."
Tokyo Olympic organisers on Thursday defended the design.
"The official emblem of the Tokyo 2020 Olympic Games captures the essence of our vision for the 2020 Games," they said in a statement.
"It will represent the Games on the world stage.
"Prior to the selection of this design, the Tokyo 2020 Organising Committee conducted long, extensive and international verifications through a transparent process."
Earlier, Japanese government spokesman Yoshihide Suga declined to make a formal comment, insisting officials had exercised due diligence prior to unveiling the logo last week.
"We are aware of the reports that the 2020 Olympic Games logo is similar to one for a Belgian theatre," he told reporters.
"Before unveiling it, we received a report that there was no problem over trademarks following investigations in Japan and abroad."
The Tokyo 2020 logo, which was unveiled last week, is based around the letter "T" - for Tokyo, tomorrow and team with a red circle representing a beating heart. It was designed by Japanese artist Kenjiro Sano.
Asked if he thought the logos were similar, Suga said with a sheepish grin: "Well I guess it varies from person to person. In any case, the government will refrain from official comment."
Embarrassingly, claims emerged that it also bore remarkable similarities to a design by Barcelona-based firm Hey Studio created in support of Japan, following the deadly quake-tsunami disaster in 2011.
The design by Barcelona-based Hey Studio bears more than a passing resemblance to the Tokyo design. Photo: Heystudio.es
On Twitter, Belgian designer Olivier Debie questioned whether Tokyo officials had been guilty of plagiarism by posting a side-by-side comparison of the Tokyo and Liege logos, tweeting: "Theatre Liege vs Tokyo 2020... #plagiat?"
He has yet to decide whether or not to pursue legal action.
"I cannot judge whether it was stolen or inspired by my work," Debie told Japan's Kyodo news. "I'm consulting with my lawyer."
The theatre's logo features a similar shape in white against a black background. "I heard the IOC (International Olympic Committee) had approved the logo and there was no special problem," said Tokyo Governor Yoichi Masuzoe.
"But if you look closely they do look alike."
Japanese officials are still smarting from the fiasco over the Olympic stadium two weeks ago when Prime Minister Shinzo Abe ordered plans to be torn up amid growing anger over its eye-watering price tag.