Emergency services are attending a major incident on the Waitaki River in the South Island.
They were called to a yachting regatta around midday, where several vessels had got into trouble on their way from the Otematata River to the Lake Aviemore Dam.
Coastguard, police and ambulance are there.
At least one person has suffered hypothermia, and police say there are likely to be more patients.
It's understood more than a dozen people are in the water.
A spokesperson for an event being held on Lake Aviemore this weekend told NZME capsizes were not unusual.
"We have a lot of safety craft there."