A 73-year-old man from Britain died and seven people were critically injured after a plane encountered severe turbulence on a flight from London to Singapore, officials said on Tuesday.

The plane, a Boeing 777-300ER operated by Singapore Airlines, was diverted to Bangkok, the airline said in an announcement on social media, and landed at 3:45 p.m. local time on Tuesday.

In all, 30 people, both passengers and crew, were injured, officials said. The airline said in a statement that 18 people had been hospitalized and another 12 people were being treated for injuries. “The remaining passengers and crew are being examined and given treatment, where necessary, at Suvarnabhumi International Airport in Bangkok,” the airline said.

The man died aboard the flight, said Kittipong Kittikachorn, the director of Bangkok’s airport, without elaborating on a cause of death. The man’s wife was injured and taken to a hospital, Mr. Kittipong said.

The flight, which had 211 passengers and 18 crew members on board, had left Heathrow Airport on Monday. The exact number of injured people on board was still under investigation, according to a statement from Suvarnabhumi Airport in Bangkok.

Emergency responders transported people with injuries to hospitals, the airport said, and set up a holding area for people from the flight who were not hurt.

The average flight time of that route is just under 13 hours. Mr. Kittipong said in a news conference that he went onto the airplane after it landed and described the scene as “a mess.”

The flight, SQ321, took off from London Heathrow at 10:38 p.m. local time on Monday. Data on Flight Radar 24, a website that compiles public information about flights, appears to show that about 11 hours later, it went from cruising at 37,000 feet to an altitude of roughly 31,000 feet in only a few minutes.

About 100 passengers who were not injured would be flown to Singapore on Tuesday, Mr. Kittipong said. He described them as being in a state of shock.

It’s unclear what caused the episode. As the plane traveled across Myanmar, satellite data showed a strong storm began to form and bubble into the higher elevations, which suggests that the atmosphere in the region was becoming unstable. The plane was also moving toward other storms developing along the coast of Myanmar.

Deaths caused by turbulence are rare. Between 2009 and 2021, 146 passengers and crew were seriously injured by turbulence, according to data from the Federal Aviation Administration. In December 2022, 11 people were seriously hurt after turbulence on a flight from Phoenix to Honolulu. In March 2023, a passenger on a business jet was killed when the plane encountered “severe turbulence.”

Chee Hong Tat, Singapore’s minister for transport, said in a statement that he was “deeply saddened to learn about the incident.”

Singapore Airlines offered its condolences to the family of the person who died on the flight, adding that “we deeply apologize for the traumatic experience that our passengers and crew members suffered on this flight.”

Judson Jones contributed reporting.