More than 100 guests at the Westin Hotel in downtown Ottawa were forced out of bed just after 4 a.m. Tuesday after a blaze broke out in an exterior air-handling unit, setting off fire alarms throughout the building.

Conference rooms on the fourth floor had to be ventilated for smoke. 

Guests were returned to their rooms within 20 minutes of being evacuated.  

No injuries were reported and damage to the building and its contents was minimal.

Fire crews are continuing to investigate the cause of the blaze.