Passengers are describing a “terrifying” Air Canada flight that hit turbulence so bad on Wednesday that it forced an emergency landing and sent 21 people to a hospital.

Connie Gelber was aboard the Shanghai to Toronto flight when the pilot ordered passengers to buckle up, despite clear skies.

After that, the plane just “dropped,” Gelber said.

“I had my seatbelt on thank goodness, but the little girl beside me didn’t,” she told CTV News Channel. “Next thing I know, she’s hitting the ceiling and then she’s down on the aisle, all the way down the aisle on the floor … She was totally injured.”

Gelber said there were “three episodes” of extreme turbulence and that the interior of the plane, “was falling apart, and everything was flying.”

“We were saying, can the plane withstand all this?”

The Montreal resident said she was worried she might never see her children again. “I thought, ‘This is it, we’re going down.’”

By the time the flight touched down in Calgary at 3:23 p.m., the plane was littered with broken tablets and cellphones, Gelber said.

“No one could find their things after,” she added. “Nobody could find their shoes to get off the plane.”

At least 21 people were sent to a Calgary trauma centre, including eight who were injured and 13 who needed observation. None of the injuries were considered life-threatening and some passengers were released from hospital Thursday.

One man described it as "all hell (breaking) loose."

“The newspapers, magazines, cellphones, glasses, blankets were just flying all over the place," he said. "And of course the screams. People were terrified."

Suzanne Caudry said she saw the passenger in front of her “fly up into the ceiling and then come down onto the floor.”

There were no doctors on board, so Caudry used her training as a periodontist to help the injured passengers, who were concentrated in the back of the plane.

“There was a mixture of people who had head and neck injuries, and there was bleeding,” she said.

“I basically gave people neck braces just to stabilize them and making them feel looked after to the best of our ability,” she added.

Caudry said she’s astounded that more people weren’t hurt. “To me, it’s a miracle we didn’t have worse happening.”

Both Gelber and Caudry said the lesson is to wear seatbelts at all times, even in clear weather. Caudry said she thinks it should be mandatory.

Airline analyst Keith Mackey advises spending as little time as possible standing in the aisles of the plane and wearing a seatbelt the rest of the time, because turbulence can happen without warning.

Although the type of turbulence associated with thunderstorms can be predicted using radar and then avoided by changing course or altitude, Mackey said “clear air” turbulence can be impossible to see coming.

The Transportation Safety Board, which has sent a team of investigators “to gather information and assess the occurrence,” also reminded air passengers Wednesday to wear their seatbelts.

Flight AC88 was travelling from Shanghai’s Pudong International airport to Toronto Pearson International Airport when it hit turbulence over Alaska. The Boeing 777-300ER was carrying 332 passengers and 19 crew members, according to Air Canada.

“Our focus today has been on those passengers who have been injured in this incident and those other passengers on the aircraft for whom this has been a very unsettling experience,” Klaus Goersch, Air Canada’s Executive Vice President and Chief Operating Officer, said in a statement.

Goersch thanked the flight crew, its employees in Calgary and the various agencies that assisted on the ground.

He said Air Canada is “grateful that the first passengers are already being released from hospital.”

With files from CTV’s Canada AM