Air Canada passengers on a plane that finally arrived in Toronto this morning, a day after a flight that had left Shanghai was diverted to Calgary, described 40 minutes of terror over severe turbulence that threw some of them into the cabin's ceiling.

An artist who goes by the name Zarum told CBC News he was sleeping and had his seatbelt on when the turbulence started during Flight 88 from Shanghai to Toronto.

"The fellow sitting in front of me went flying up, hit the ceiling and came flying down," he said. "Everything went flying: newspapers, blankets, cellphones, glasses. They were just flying all over the place.

"During the peak moment, you could hear screams all the way to the back of the plane," he said. "You could hear in the galley things flying and breaking."

Flight 88 diverted to Calgary after encountering the turbulence over Alaska.

Twenty-one passengers — including three children — were taken to hospital in Calgary, where they were treated for multiple injuries, none life-threatening. 

The flight arrived at Toronto's Pearson International Airport at 3 a.m. ET Thursday. 

Passengers who spoke to CBC News were still shaken up. 

"There was a gentleman in front of us that literally hit the roof," said Dr. Suzanne Caudry, a periodontist who helped injured passengers. "There were people with head and neck injuries, there was bleeding," she said. 

She praised Air Canada staff for helping injured passengers who had to wait an hour before the plane was able to land in Calgary.

"The ceiling literally fell down," said passenger Elizabeth Brayton, who was awoken when the plane began to bounce. "There was a lot of screaming and a lot of kids crying."

'If there's a message here, it's wear your seatbelt'

Zarum said that after the turbulence ended, the cabin was in disarray. 

"You could see part of the ceiling, where somebody had actually flown into it and broken the plastic," he said. "The gas masks were hanging down. Blood. People were looking for lost items and trying to calm down."

Caudry said passengers were told by an announcement in the cabin to put on their seatbelts before the severe turbulence started. The ones who didn't or those who were sleeping and didn't hear the message appeared to have suffered the most serious injuries. 

"If there's a message here, it's wear your seatbelt," she said. "I think it should be mandated that you wear them at all times."

Dr. Suzanne Caudry

Passenger Suzanne Caudry, a periodontist, worked to help some of the passengers injured when the Shanghai to Toronto flight encountered severe turbulence. (CBC)