Lucas Oleniuk via Getty Images A Porter AIrlines aircraft similar to the one in this image took evasive action on Monday to avoid an unidentified flying object, possibly a drone or balloon, while descending into the Toronto area.

Two people suffered minor injuries after an aircraft swerved to avoid a “UFO” in the skies over Lake Ontario on Monday.

The Porter Airlines Dash 8 aircraft, which was carrying 54 passengers, encountered the object at about 9,000 feet as it descended into the Billy Bishop Toronto City Airport.

“The pilots noticed an object in the distance (and) as they approached the object, they realized it was very close to their flight path,” Porter Airlines said in a statement, according to the Canadian Press.

At first the pilots thought it was a balloon. However, after debriefing, they said the object could have been a drone.

“Nobody knows at this point. It happened so quick,” Peter Rowntree, senior regional investigator with the Transportation Safety Board of Canada, told The Star. “It definitely wasn’t a bird. It was a fairly large object.”

Two flight attendants were taken to an area hospital to be treated for minor injuries, the CBC reported.

The Canadian government is now working to pass new rules to regulate the growing number of drones, and possibly help prevent incidents such as this one.

There have been a number of close calls between aircraft and drones around the world, especially near airports. Fortune reported in March that the FAA had seen an increase in reports of possible encounters with unmanned vehicles, with 583 between Aug. 22, 2015, and Jan. 31, 2016, compared to 238 in all of 2014.

CORRECTION: This article previously referenced an April report of an incident at Heathrow involving a British Airways flight. Authorities later determined there was no evidence a drone was involved, according to the BBC.