A British grandfather is dead and dozens are now in hospitals in Bangkok, including eight Australians, after a flight from the UK to Singapore hit severe turbulence, plunging 1,800 metres (6,000 feet) in a few minutes.

Passengers onboard the Singapore Airlines plane told of the “dramatic drop”, which launched those not wearing a seatbelt into the cabin ceiling, resulting in the 73-year-old British passenger’s death, with several others critically injured, and leaving many others with head wounds and broken limbs and bleeding flight staff, surrounded by debris scattered around the cabin.

Singapore Airlines flight SQ321 took off from London Heathrow on Monday night (early yesterday AEDT) before it hit clear air turbulence – which is harder to detect or forecast – and was diverted to Bangkok where it landed yesterday afternoon.

The airline said the Star Alliance liveried Boeing 777 was carrying 211 passengers – including 56 Australians, plus passengers from Britain, New Zealand and Singapore – and 18 crew.

“Flight SQ321 encountered sudden extreme turbulence over the Irrawaddy basin … The pilot declared a medical emergency and diverted the aircraft to Bangkok,” the airline said in a statement.

“Singapore Airlines offers its deepest condolences to the family of the deceased. We deeply apologise for the traumatic experience that our passengers and crew members suffered on this flight. We are providing all necessary assistance during this difficult time. We are working with our colleagues and the local authorities in Thailand to provide the necessary assistance.”

The deceased passenger has been identified as Geoffrey Kitchen, 73, from Thornbury, Gloucestershire, a retired insurance professional.

Kitchen and his wife were on their way to a holiday in Australia via Singapore. Thai authorities sated that he had a heart condition and likely died of a heart attack.

Airports of Thailand general manager Kittipong Kittikachorn confirmed the death and said seven others were in a critical condition, mostly with head injuries. Twenty-three passengers, plus one crew member, had less severe injuries, he told of a press conference.

“The incident happened during meal service, about two to three hours before the flight was due to land in Singapore,” he added. “It was probably during breakfast service. Most of the passengers had fastened their seatbelts.”

Emergency services met the plane at Bangkok’s Suvarnabhumi airport. A local police officer at Samitivej Srinakarin hospital in Bangkok, where the injured were brought, said he had seen about 70 wounded people, including some with very minor conditions. Some patients requested to be taken to another hospital. One man was brought out on a stretcher to be transferred via ambulance. Another was brought out in a wheelchair.

Injured passengers met by fleet on ambulances

Terrified passengers were met by a fleet of ambulances ion the tarmac at Suvarnabhumi airport.

“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,” passenger Dzafran Azmir 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.”

Another passenger told BBC Radio 5 Live: “During the few seconds of the plane dropping there was an awful screaming and what sounded like a thud.”

He said he had helped a woman “screaming in agony” who had a “gash on her head”.

Another told of passengers who had been walking around the cabin “doing somersaults” during the tubulence.

Boeing ‘ready to support’ passengers

Singapore Airlines released details of the passenger manifest which confirmed the passengers onboard as 56 from Australia, two from Canada, one from Germany, three from India, two from Indonesia, one from Iceland, four from Ireland, one from Israel, 16 from Malaysia, two from Myanmar, 23 from New Zealand, five from the Philippines, 41 from Singapore, one from South Korea, two from Spain, 47 from the United Kingdom and four from the US.

Boeing, manufacturer of the 777-300 aircraft , said it “stood ready to support” Singapore Airlines.

Boeing added: “We extend our deepest condolences to the family who lost a loved one, and our thoughts are with the passengers and crew.”

Deaths caused by turbulence are extremely rare on international scheduled flights. But severe injuries during turbulence are not uncommon.