A Hawaiian Airlines flight encountered severe turbulence Sunday that left 36 people injured, 11 of them seriously.

According to Hawaii News Now, flight 35 was traveling from Phoenix to Honolulu when it hit a pocket of severe turbulence around 30 minutes prior to its scheduled landing. The turbulence was so strong, some passengers flew out of their seats.

Before the plane’s landing, paramedics and firefighters reported to the airport to respond to what was labeled a “mass casualty emergency.” Upon landing, they met the airplane at the gate and treated passengers as young as 14 months old.

Injuries sustained in the turbulence include cuts, bruises, serious head injuries, and loss of consciousness. Twenty of the injured were transported to emergency rooms. Nine of them were in stable condition and 11 were in serious condition.

According to Hawaiian Airlines, the flight landed in Honolulu around 10:50 a.m. The airline’s executive vice president and chief operating officer Jon Snook said the “fasten seatbelt” was on when the turbulence struck. He also said that among the injured people were three flight attendants.

“Sometimes, these air pockets occur with no warning, he said. “It’s rare to have that level of extreme turbulence. It was a very extreme case of mid-air turbulence. We’re very thankful the extent of the injuries was not critical. It could have been worse.”

According to the National Weather Service, the turbulence occurred at around 36,000 feet.

“We believe the flight may have gone through a thunderstorm, which may have caused the severe turbulence. During that time, there were scattered thunderstorms everywhere,” NWS meteorologist Genki Kino said.

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