One person died and dozens of others were left injured after a Singapore Airlines flight encountered "severe" turbulence, the airline said in a social media post.
The Boeing 777-300ER departed London's Heathrow Airport on Monday with 221 passengers and 18 crew members on board, according to the airline.
The flight, SQ 321, encountered turbulence about 90 minutes from its destination of Singapore and was diverted to Bangkok, the carrier said.
Six people were critically injured, Kittipong Kittikachorn, general manager for Bangkok's Suvarnabhumi Airport, said. Dozens of other passengers suffered minor or moderate injuries, he said.
MORE: Iowa governor declares disaster emergency as tornadoes rip through 15 countiesGeoff Kitchen, a 73-year-old man from the U.K., died, according to authorities and a music theater group where he worked.
The U.K.-based Thornbury Musical Theatre Group said in a Facebook post, "Geoff was always a gentleman with the utmost honesty and integrity and always did what was right for the group. His commitment to TMTG was unquestionable and he has served the group and the local community of Thornbury for over 35 years, holding various offices within the group, including Chairman, Treasurer and most recently Secretary. Our thoughts and prayers go out to his wife and the family at this difficult time, and we ask that you respect their privacy."
Singapore Airlines offered its condolences to Kitchen’s family.
"Singapore Airlines offers its deepest condolences to the family of the deceased," the airline said in a statement on Tuesday. "Our priority is to provide all possible assistance to all passengers and crew on board the aircraft."
The National Transportation Safety Board said it was sending a team to assist in the investigation.
"Suddenly, the aircraft starts tilting up, and there was shaking, so I started bracing for what was happening, and very suddenly there was a very dramatic drop, so everyone seated and not wearing a seatbelt was launched immediately into the ceiling," Dzafran Azmir, a 28-year-old student on the flight, told ABC News. "Some people hit their heads on the baggage cabins overhead and dented it; they hit the places where lights and masks are and broke straight through it."
MORE: Father, 2 siblings set to graduate from college killed after small plane crashes in TennesseeSingapore Airlines CEO Goh Choon Phong addressed the SQ321 incident in a video.
"We are deeply saddened by this incident, and are committed to providing all necessary support and assistance to the passengers and crew members who were on board SQ321, as well as their families and loved ones. Our deepest condolences go out to the family and loved ones of the passenger who passed away," Phong said.
The airline said late Tuesday night that four of the passengers were American. Two of them were injured.
The aircraft appeared to have encountered the turbulence in Thai airspace, somewhere over the Andaman Sea.
The flight, which had been scheduled to arrive at Singapore Changi Airport, instead touched down in Thailand at about 3:45 p.m. local time, the carrier said.
"We are in contact with Singapore Airlines regarding flight SQ321 and stand ready to support them," Boeing said in a statement. "We extend our deepest condolences to the family who lost a loved one, and our thoughts are with the passengers and crew."
ABC News' Joe Simonetti, Will Gretsky and Helena Skinner contributed to this report.