A "flight from hell" from China to Canada was diverted after heavy turbulence injured 21 passengers, including three children.

Emergency Medical Services spokesman Stuart Brideaux said those taken to hospital after the Shanghai to Toronto flight made an unscheduled landing in Calgary were in a stable condition with neck and back injuries.

Fire crews and other emergency services were waiting when the plane landed at around 3.30pm (10.30pm Irish time) on Wednesday.

Passenger Connie Gelber told the Calgary Herald the journey had been "the flight from hell" and added: "It was frightening. Honestly we didn't know if we were going to live or die."

She said the girl sitting beside her was thrown "right out of her seat down the aisle" when the turbulence hit.

Bing Feng said: "It was just like you were in a roller coaster. The plane was just going down like very straight, straightly, like, go down. And lots of screaming."

Air Canada said the Boeing 777 - carrying 332 passengers and 19 crew members - landed without incident.

The airline said it would be making arrangements to accommodate the other passengers, including those continuing on to Toronto, and that the incident was being investigated.

There was no immediate indication of what caused the turbulence.