About a quarter of the population of 127 million live in Tokyo and surrounding prefectures.
The congested megalopolis thus faces a serious need to ease rush-hour crowds to accommodate tourists for the Olympics.
The public-private "Telework Day" involved some 60,000 workers at more than 900 companies, organisations and government offices, according to the internal affairs ministry.
They worked from home, skipping their usual habit of commuting in notoriously packed trains or driving personal cars to the office.
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The idea followed a teleworking effort at the time of the 2012 London Olympics. Japan will repeat the exercise on the same date over the next two years in the run-up to the opening of the Summer Games on July 24, 2020.
The plan is also part of Prime Minister Shinzo Abe's efforts to rethink Japan's workaholic tradition, where mostly male workers are routinely expected to spend long hours in the office and have little time with their families.
"Teleworking can be one solution" to heavy traffic congestion in the Tokyo metropolitan area, said a government official in charge of the campaign.
"Some people may say they felt some effect (on reducing congestion) this morning, while others say they felt no difference.
"This is a small start but we'd like it to trigger companies as well as workers to start thinking about a different work style," he said.
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