"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," the airline said, adding it was working with Thai authorities to provide all necessary assistance.
One male passenger died, Kittipong Kittikachorn, director of Bangkok's Suvarnabhumi airport, told Reuters.
Eighteen people have been hospitalised and 12 were being treated in hospitals, Singapore Airlines said.
It was not immediately possible to reconstruct the incident from publicly available tracking data, but a spokesperson for FlightRadar 24 said it was analysing data that showed the plane tilting upwards and return to its cruising altitude over the space of a minute.
Ambulances arrived on the tarmac to carry passengers from the flight after it landed in Bangkok. (AP PHOTO)
A passenger who was on the flight told Reuters 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."
The spokesperson for FlightRadar 24 said "our initial thinking is the turbulence event is prior to the standard descent from 37,000 to 31,000 feet (11,300 metres to 9400m)".
"That appears to just be a flight level change in preparation for landing."
The Boeing 777-300ER plane with 211 passengers and 18 crew was headed to Singapore when it made the emergency landing, the airline said.
Singapore news outlet CNA carried blurry pictures supplied by readers that it said appeared to be from the flight.
They showed anxious passengers clinging to seats, with oxygen masks hanging from above, personal items strewn across the aisle and rubbish spilled on the floor of the cabin crew area.
Suvarnabhumi airport said the plane requested an emergency landing at 3.35pm, local time, and landed at 3.51pm.
Uninjured passengers disembarked and an another aircraft will fly them onwards.
The airline said it landed at 3.45pm.
Turbulence-related airline accidents are the most common type, according to a 2021 study by the 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.
Singapore Airlines, which is widely recognised as one of world's leading airlines and is a benchmark for much of the industry, has not had any major incidents in recent years.
Its last accident resulting in casualties was a flight from Singapore to Los Angeles via Taipei, where it crashed on October 31, 2000, into construction equipment on the Taiwan Taoyuan International Airport after attempting to take off from the wrong runway.
The crash killed 83 of the 179 people on board.
Boeing did not immediately respond to a request for comment.
