Singapore Airlines has tweaked its in-flight seatbelt sign policies and altered at least one flight route after a turbulence incident this week killed one person and left dozens more hospitalised, according to the airline and flight data.

The airline is adopting a more cautious approach to turbulence, including not serving hot drinks or meals when the seat belt sign is on, it said in a statement to Singapore broadcaster Channel News Asia.

"SIA will continue to review our processes, as the safety of our passengers and crew is of utmost importance," it said.

The airline did not respond to a Reuters request for comment.

The SQ321 London-Singapore flight on a Boeing 777-300ER plane carrying 211 passengers and 18 crew diverted to Bangkok for an emergency landing on Tuesday after the plane was buffeted by turbulence that flung passengers and crew around the cabin, slamming some into the ceiling.

The daily London to Singapore route SQ321 has completed two flights since the incident and not flown over the part of Myanmar where the sudden turbulence occurred about 3 hours before scheduled landing. The flight time is about the same, tracking data show.

They flew instead over the Bay of Bengal and Andaman Sea, route data from flight tracker FlightRadar 24 shows.

Singapore Airlines has said the plane on Tuesday encountered sudden extreme turbulence. A 73-year-old British passenger died of a suspected heart attack.

Photographs from inside the plane showed gashes in the overhead cabin panels, oxygen masks and panels hanging from the ceiling and luggage strewn around. A passenger said some people's heads had slammed into the lights above the seats and broken the panels.

As of late Thursday, 46 passengers and two crew members were hospitalised in Bangkok; 19 others were still in Bangkok, the airline said.

Twenty of the 46 remained in intensive care, an official at Bangkok's Samitivej Srinakarin Hospital said on Thursday, adding that the injured had a mix of spinal cord, brain and skull injuries.

Singapore Airlines, which is widely recognised as one of the world's leading airlines and is seen as a benchmark for much of the industry, has not had any major incidents in recent years.