The group were due to play a matinee and evening show at the SSE Arena in Belfast.
The cancellation announcement came just minutes after the doors opened for the afternoon performance.
Fans have been left angry and disappointed at the short notice that the gigs were off.
Many had travelled from across the province to the shows.
Those attending have been advised by Aiken Promotions to hold onto their tickets as the gigs could be rescheduled.
Details of new dates are expected to be announced later, say the promoters.
In a message on the Twitter feed, Little Mix stated: