MTR controllers went into emergency mode after a taxi was spotted on a Light Rail track in Tuen Mun.
No one was hurt and the driver drove off after MTR personnel rushed to the scene and ordered him to leave, news website hk01.com reports.
An MTR spokesman confirmed the incident and said the driver will be served with a warning letter.
Engineers said there was no damage to the tracks.
Pictures of the wayward cab have gone viral on social media, sparking wild theories about how it got there.
Some netizens said the driver might have been unfamiliar with the roads in Tuen Mun and used the tracks to find his way.
Others said he might have thought vehicles can share the tracks with rail cars as they do on Hong Kong Island with trams.
But many could not miss the unusual sight.
They said the scene was something straight out of Grand Theft Auto, an action-adventure video game with plenty of wild car racing and stealthy competition set in a fictional city.
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