Two flight attendants sustained minor injuries when a plane headed from Ottawa to Toronto performed a sudden dive Monday morning, to avoid a mid-air collision with an unidentified object.

The Porter Airlines flight was 30 nautical miles east of Toronto, near Pickering Ont., and flying at 9,000 feet “when the pilots noticed an object in the distance,” according to the airline.

“As they approached the object, they realized it was very close to their flight path and decided to take appropriate evasive action,” the airline says. “There was no contact between the aircraft and object.”

“The pilots’ initial assessment was that it looked like a balloon,” the airline’s statement goes on. “After debriefing, there is potential that the object was a drone.”

The Transportation Safety Board has deployed two investigators to Toronto’s Billy Bishop City Centre Airport.

Spokesperson Peter Rowntree said the pilots caught only a “brief glimpse” of the object before putting the aircraft into a dive.

“Honestly, there’s no idea what it was they saw,” Rowntree said, adding it “could be a drone, could be a balloon … could be a piece of garbage.”

Tony Di Benedetto, CEO of Drone Delivery Canada, said he believes that it could have been a hobbyist’s drone.

Many consumer drones have software locks that limit how high they can fly, but they can be modified to “go as high as you, potentially, want … maybe to 10,000 or 20,000 feet,” according to Di Benedetto.

He points out that drones are often used for photography, so one theory is that it was a photographer trying to capture the extra-bright “supermoon” at sunrise. The moon made its closest approach to earth in 69 years Monday, peaking at 6:21 a.m. ET.

Still, Di Benedetto points out most consumer drones are so small that they would be difficult for pilots to see.

One possibility, according to Rowntree, is that it was a Canadian or U.S. military drone.

Transport Canada says drones should not be flown more than 90 metres (300 feet) above the ground or within nine kilometres from any airport or helipad. Earlier this year, Transport Canada said that it had investigated about 50 incidents involving unmanned aerial vehicles between 2010 and the end of 2015.