Two teenage boys and a woman in her 30s are understood to be among those injured after scores of dinghies capsized on Strangford Lough today.
It is believed the woman suffered an injured arm and that one person was in the water for about 20 minutes.
Sailors from north and south of the border, England and Australia were taking part in the competitions.
Two races had been due to be held today but only one was completed before the squall struck with the dozens of boats competing off islands about three miles offshore.
Within two hours of the initial reports of the capsized boats health chiefs said they called off the major incident response at the Ulster Hospital.
Organisers of the GP14 had attempted to begin racing yesterday. However, the event was called off ater they put out on to the water when rain and strong winds associated with the tail end of former Hurricane Bertha created choppy seas.
Organisers said the conditions "caught out some of those less used to the lough".
Four boats capsized on Sunday and two suffered damaged rudders before the competition was postponed.