The plane was carrying 163 passengers and 12 crew members on Thursday when it “encountered unexpected severe turbulence approximately five hours into the flight,” said a statement from the airline.

“The plane just dropped,” passenger Sultan Baskonyali told ABC News. “We weren’t prepared.”

She described one man going upward, hitting his head on the ceiling and dropping back down.

Airport medics assessed and released three injured passengers when the flight landed in Sydney, the airline said. One passenger and three flight attendants were referred to hospitals for evaluation. The flights attendants have since been released, the airline said Monday, but added that it was waiting to hear from the passenger.

“I haven’t heard from the airline at all even though both my children who were on the flight sustained minor injuries,” another passenger, Tara Goodall, told The Associated Press Monday.

They were returning home to Sydney after visiting Hawaii — the first overseas trip for her two sons. It was difficult, she said in text messages, “seeing your kids being thrown around the plane cabin” and being unable to make them feel safe.

She said she wasn’t yet ready to discuss the turbulence in more detail because she was still upset and emotional about it.

“Our immediate priority is to continue to care for our passengers and crew affected by this turbulence event, and we thank Sydney airport first responders for their swift assistance,” the airline said.

Last year, severe turbulence injured 25 people on board a Hawaiian Airlines flight. Four passengers and two crew members were seriously hurt. The plane sustained minor damage.

The captain of the Dec. 18 flight from Phoenix to Honolulu told investigators that conditions were smooth with clear skies when a cloud shot up in front of the plane, and that there was no time to change course, according to a report by the National Transportation Safety Board.

Hawaiian Airlines Chief Operating Officer Jon Snook said at the time that such turbulence is unusual, noting that the airline had not experienced anything like it in recent history. The sign to fasten seatbelts was on at the time, though some of the people injured were not wearing them, he said.

It happened about 40 minutes before landing in Honolulu, according to the NTSB report.