Bad weather on Sunday morning affected two running events - the inaugural Kranji Countryside Run and the adidas King of the Road event.
The competitive 8km route at Singapore's first countryside run was cancelled "in order to prevent runners from slipping on the wet pavement in their haste to clock a good timing," said president of the Kranji Countryside Association Ivy Singh-Lim.
Competitive runners, however, could still take part in the 4km fun run, which took place as scheduled. The wet weather also pushed back the 8.15am flag-off timing to 8.50am.
At the adidas race, however, both the 10km and 16.8km events were cancelled before flag-off due to safety concerns posed by heavy rain and lightning.
Some 11,000 participants were affected, but organisers said no refunds will be issued as participants were informed about the no-refund policy during registration.