Six tourists were swept away by a flash flood when they were river tracing in New Taipei City, according to the local fire department.
The four adults and two teenagers were all wearing life jackets and helmets during the activity, which is also known as canyoning, on a river in Pinglin District.
They were part of a group of 24 people participating in the activity. Eighteen others were safe.
Pinglin District experienced heavy rain at midday on Sunday, with more than 100 mm falling within one hour.
Dozens of ambulances and rescue vehicles, and a helicopter were dispatched to the scene.
The search continues.
