"This is a shocking and upsetting incident. Our thoughts are with the audience and staff who were in the theatre and their families.
"We're very grateful to the emergency services for their tremendous work and to our staff who helped with the evacuation."
Performances of The Curious Incident of the Dog in the Night-Time, which was playing when the incident occured, have been cancelled up to and including Saturday 4 January 2014.
Ticket holders are advised to contact their original point of purchase.