SINGAPORE — A Singaporean family newly relocated to Vietnam have alleged that Singapore Airlines (SIA) caused their dog's death two Saturdays ago, and said they had filed a police report to take the airline to task for apparent negligence.

Their four-year-old cocker spaniel, Charlie, was supposed to board a two-hour flight to Ho Chi Minh City on Sept 2 but died in its crate while being transferred to the aircraft at Changi Airport, a SIA spokesperson confirmed on Sunday (Sept 10).

Charlie belonged to Ms Shabana Mary Kuruvilla, who arranged for her dog to fly with her family in a crate. But only in Vietnam did SIA inform them of the dog's death.

She shared her account on Facebook on Thursday, and her post has since garnered more than 900 shares, with netizens expressing shock and concern over the incident.

According to her, airline staff told her family at the boarding gate that their pet dog was "a bit anxious" and "had some mucus", and asked if they wanted to see it.

But they did not, thinking that "mucus or saliva is a very normal thing for a dog, and we felt we shouldn't make him more anxious just before boarding", she wrote. "They never told us that our dog was severely distressed."

After they boarded, the captain announced that a pet was on board the aircraft, leading them to feel assured that everything was okay, Ms Shabana added.

But when they asked to see Charlie upon landing, a staff member told them that the dog did not board and had died in Singapore, Ms Shabana said.

The family was told that disclosure was not made before the flight took off because "the gates had closed and they didn't want to delay the flight".

"Charlie's death took us by complete shock. We questioned how the captain made the announcement about the pet on the aircraft when Charlie had not boarded. They said there was no time to inform him."

Ms Shabana and her husband took the next available flight back and retrieved Charlie from Changi Airport's lost-and-found corner, where they found that it had chewed up a portion of its wee pad, made of cotton, before it died.

The family believes that it suffered a heart attack from stress. There was also blood on its paw and mouth - a sign that it was trying to break open the crate "in desperation", said Ms Shabana.

An investigation is ongoing, said an SIA spokesperson. "For privacy purposes, we're unable to share further details," he told TODAY, adding that the airline will contact the family to share its findings once investigations are completed.

"We wish to express our sincere condolences to the owners at this time."