The Transportation Safety Board says a WestJet flight headed for Vancouver was forced to perform an emergency landing in Calgary after a small fire broke out on board.

Shortly after takeoff on Thursday morning, crew members on WestJet Flight 113 headed from Calgary to Vancouver were alerted by a fire indication light in the cargo hold. The Boeing 737 then turned back for an emergency landing.

WestJet says the plane landed safely and all of the passengers were booked on another flight.

“We sincerely apologize for the delay and inconvenience to our guests but safety is always our first priority,” the airline said in a statement.

Chris Krepski, spokesperson for the Transportation Safety Board, said once airport firefighters went into the cargo hold, they found a fire-damaged bag. There’s no indication yet what caused the fire.

Krepski said TSB investigators would be arriving to the airport on Thursday afternoon to begin their investigation.

“We’re going to examine the aircraft, examine the bag (and) interview witnesses and flight crew to gather information,” he said in a phone interview. “From there we’ll decide what our next steps will be.”