Olympic Games organisers have started rescheduling events after reports indicate that typhoon Nepartak is approaching Tokyo, the host city.
It is expected to make landfall on Tuesday.
Typhoon Nepartak, known in the Philippines as Typhoon Butchoy, was the third most intense tropical cyclone worldwide in 2016.
It severely impacted Taiwan and East China, with 86 confirmed fatalities.
Weather authorities warned of heavy rains, gale-force winds and high waves which could already affect the region from Monday onwards.
Rowing had all Monday events moved to Sunday, and Tuesday has also been cleared with events moved to Wednesday.
Other outdoor sports could follow as organisers are in close contact with sports federations about rescheduling and changing of the programme.
For now, athletes were mainly dealing with high temperatures and humidity.
Tennis on Sunday applied its extreme heat rules with longer changeover breaks and a 10-minute break before the third set.
NAN
