Airline spokesman Robert Palmer says the flight was carrying 95 passengers and six crew members and took off from Edmonton at 7 a.m. local time.
Palmer says about two and a half hours later, the captain reported possible smoke in the cabin and decided to divert the flight to Thunder Bay.
He says an emergency was declared as a precaution to ensure a priority landing and to have emergency vehicles on scene to meet the plane.
The Boeing 737 landed without incident and maintenance crews are currently examining the aircraft.
Palmer says passengers were taken into the airport terminal and are expected to complete their journey on other WestJet flights heading to Toronto this afternoon.
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