One person has died and at least 30 others were injured after a Singapore Airlines flight hit “severe turbulence” during a transcontinental journey, the airline said Tuesday.

The flight, SQ 321, was traveling from London to Singapore, a trip that typically takes about 13 hours. The plane diverted to Bangkok and landed at 3:45 local time (4:45 a.m. ET) Tuesday.

Eighteen people have been hospitalized and another 12 are receiving medical treatment, the airline said. The rest of the passengers and crew members were being examined at Suvarnabhumi International Airport in Bangkok.

The airport’s general manager, Kittipong Kittikachorn, said at a press conference that the person who died was a 73-year-old British man, likely from a heart attack, Reuters reported. Seven others were critically injured with head wounds.

“Singapore Airlines offers its deepest condolences to the family of the deceased,” the company said. “We deeply apologise for the traumatic experience that our passengers and crew members suffered on this flight.”

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There were 211 passengers and 18 crew members on board the Boeing 777-300ER plane, according to the airline. Kittikachorn said the plane fell into an air pocket during breakfast service before it hit turbulence.

Data from FlightAware, which tracks flights in real time, indicates that the plane experienced a drastic drop in altitude about 11 hours into the flight, losing approximately 6,000 feet within four minutes as it plunged to 31,000 feet from its cruising altitude of 37,000 feet. The plane diverted to Bangkok shortly after.

Singapore Airlines has consistently been ranked as one of the safest airlines in the world. Worldwide, severe turbulence has previously caused mass injuries on flights — and at least one death — in the last year. At least one recent study suggests that clear-air turbulence, which is associated with wind shear, is getting more prevalent because of climate change.