There were a total of 211 passengers and 18 crew on board, it said.
The nationalities of the passengers are as follows: 56 from Australia, 2 from Canada, 1 from Germany, 3 from India, 2 from Indonesia, 1 from Iceland, 4 from Ireland, 1 from Israel, 16 from Malaysia, 2 from Myanmar, 23 from New Zealand, 5 from the Philippines, 41 from Singapore, 1 from South Korea, 2 from Spain, 47 from the United Kingdom, and 4 from the United States of America.
Authorities have not released details of the injured passengers and crew or their nationalities.
"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," it said.
Singapore Airlines was using a 16-year-old 777 model for the SQ321 service hit by severe turbulence.
A Singapore Airlines team is on its way to Bangkok to provide any additional assistance needed. SIA is working with the relevant authorities on the investigation into this incident.
Relatives seeking information may call the Singapore Airlines hotlines at +65 6542 3311 (Singapore), 1800-845-313 (Australia), and 080-0066-8194 (the United Kingdom), the carrier said.
Singapore's new Prime Minister Lawrence Wong extended his condolences to “family members and loved ones of the deceased.” “Unfortunately, we are marking Vesak Day this year with news of the incident on the SQ321 flight earlier today. We are all saddened and shocked by what happened,” he said in a Facebook post.
He added that Singapore is working closely with the Thai authorities and “doing everything we can to support the passengers and crew”.
“We pray for their safe return and smooth recovery for those who are injured. We are still getting more information from Bangkok and will provide further updates in due course,” he said.
US aircraft manufacturer Boeing extended its condolences to the family of the British man who died aboard SQ321, a Boeing 777-300ER.
“We are in contact with Singapore Airlines regarding flight SQ321 and stand ready to support them,” Boeing said on X.
With light and moderate turbulence passengers might feel a strain against their seatbelt, and unsecured items could move around the cabin. But in severe cases turbulence can throw passengers around the cabin, causing severe injuries and occasionally death, CNN reported.