Aftermath video showing the cabin of Singapore Airlines flight SQ321 after experiencing severe turbulence that killed one person.

SINGAPORE: One passenger was killed and scores injured, some critically, after a Singapore Airlines (SIA) flight from London to Singapore encountered severe turbulence.

SQ321, which left London's Heathrow Airport at 10.38pm local time on Monday (May 20), had to make an emergency landing in Bangkok.

A 73-year-old British man died during the incident, likely due to a heart attack, Suvarnabhumi Airport general manager Kittipong Kittikachorn told a press conference.

The plane fell into an air pocket while the cabin crew were serving breakfast before it encountered turbulence.

Seven people were critically injured with head injuries, but people were calm as they were led from the plane, Kittikachorn added.

Eighteen people have been hospitalised and 12 are being treated in hospitals, said SIA. A total of 211 passengers and 18 crew members were on board the Boeing 777-300ER.

An SIA team was also on the way to Bangkok to provide additional assistance.

"Our priority is to provide all possible assistance to all passengers and crew on board the aircraft," said SIA.

"We are working with the local authorities in Thailand to provide the necessary medical assistance, and sending a team to Bangkok to provide any additional assistance needed."

Singapore's Transport Safety Investigation Bureau (TSIB), an arm of the Transport Ministry, is opening an investigation into what happened on SQ321.

It says it has been in contact with its Thai counterparts and will send investigators to Bangkok.

SIA said it was over the Irrawaddy Basin in Myanmar at 37,000 feet that the plane encountered "sudden extreme turbulence". This took place 10 hours after departure from Heathrow.

The pilot then declared a medical emergency and diverted the plane to Bangkok, where it landed at Suvarnabhumi Airport at 3.45pm local time (4.45pm Singapore time).

A passenger who was on the flight told Reuters that the incident involved the sensation of rising then falling.

"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 board the flight told Reuters.

"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," he said.

Kittikachorn, the Thai airport official, said most of the passengers he had spoken to had been wearing their seatbelts.

Photographs from the interior of the plane showed large gashes in the overhead cabin panels, gas masks and panels hanging from the ceiling and items of hand luggage strewn around. A passenger said some people's heads had slammed into the lights above the seats and punctured the panels.

"I saw things lying everywhere and many aircrew injured" with bruising, Kittikachorn said after the most critically injured passengers and crew had been evacuated.

Turbulence-related airline accidents are the most common type, according to a 2021 study by the US National Transportation Safety Board.

From 2009 through 2018, the US agency found that turbulence accounted for more than a third of reported airline accidents and most resulted in one or more serious injuries, but no aircraft damage. The NTSB is sending representatives to support Singapore's investigation into the incident, it said.

Singapore's Ministry of Foreign Affairs (MFA) said it has been in contact with SIA, and the relevant Singapore and Thai authorities to coordinate assistance for the passengers and their families.

Staff from the Singapore Embassy in Bangkok are also at Suvarnabhumi Airport and the hospital to offer consular assistance to affected Singaporeans and their next-of-kin, it added.

"MFA extends our deepest condolences to the family of the deceased passenger and we wish those injured a quick and full recovery."

Singapore President Tharman Shanmugaratnam expressed his condolences to the family and loved ones of the person who died on board SQ321.

"We must hope and pray that the passengers or crew members who were injured are able to recover smoothly," he wrote on Facebook.

Boeing said it was in touch with Singapore Airlines and was ready to provide support. It referred further questions to the airline and local authorities.

"We extend our deepest condolences to the family who lost a loved one, and our thoughts are with the passengers and crew," it said.

Transport Minister Chee Hong Tat also expressed his condolences. He added that the authorities and SIA staff are providing support to the affected passengers and their families.

CNA has reached out to SIA for more information.