There were 211 passengers and 18 crew on board the Boeing 777-300ER.
The Boeing 777-300ER was diverted to Bangkok, where it landed at 3:45pm (08:45 GMT) on Tuesday.
Flight SQ321 “encountered severe turbulence en route”, Singapore Airlines said in a statement on its Facebook page.
“We can confirm that there are injuries and one fatality on board the Boeing 777-300ER.”
There were 211 passengers and 18 crew on board.
“Our priority is to provide all possible assistance to all passengers and crew on board the aircraft”, the airline said.
“We are working with the local authorities in Thailand to provide the necessary medical assistance.”
A spokesperson for Bangkok’s Suvarnabhumi Airport said that a medical team was on standby.
Singapore Airlines did not say how many people were injured, but multiple Thai media reports said there were 30 injured.
Singapore’s Transport Minister Chee Hong Tat said the government would provide assistance to the passengers and their families.
“I am deeply saddened to learn about the incident onboard Singapore Airlines flight SQ321 from London Heathrow to Singapore,” he posted in a statement on Facebook. “My deepest condolences to the family of the deceased.”
More to come …