At least 17 people were hurt in powerful turbulence encountered by a flight from Frankfurt, Germany, to Shanghai on Monday.

Air China flight CA936 was scheduled to take off at 8 pm Frankfurt time (2 am in China) and arrive at Shanghai Pudong International Airport at 12:55 pm－a flight of approximately 11 hours.

The flight encountered severe turbulence as it entered the Shanghai region that resulted in injuries to four male and 13 female passengers, including a senior German couple above age 70. The injuries to one of the females was serious, said a report on eastday.com.

The injured were "passengers who did not buckle up and stewards who were patrolling the cabin and serving passengers", a statement from Air China to China Daily said.

"The crew sent an emergency notice to the ground immediately," it said, and ambulances took the injured to Pudong New Area People's Hospital for medical treatment immediately upon landing.

By 2 pm on Monday, four passengers and two flight attendants remained hospitalized for observation and treatment. Two other passengers were discharged.

"Thunderstorms are taking place often nationwide at the moment, so it is common for aircraft to encounter severe turbulence. Passengers are requested to fasten their seat belts throughout the flight," said Li Lei, an industrial analyst who specializes in aviation research at Beijing-based Minzu Securities.

On an Air Canada flight en route from Shanghai to Toronto in December, at least 20 people, including 3 children, were hurt in heavy turbulence, Xinhuanet.com reported.

"The continuous expansion of aviation companies' fleets has also increased the number of encounters with turbulent air in flight, but meteorological forecasts are also becoming more precise," Li said.

For passengers, having the seat belt fastened is the primary precaution available, with or without a turbulence warning from the crew.

Data from several severe incidents of turbulence showed that virtually all the people seriously injured were passengers who failed to buckle up or crew members who were serving passengers in the cabin, Xinhuanet reported.