A passenger on a United Airlines flight from Denver to Salt Lake City died on the plane on Sunday. The unidentified man passed away on flight 5596 and the exact cause of death is currently unknown, according to The Salt Lake Tribune.

Authorities at Salt Lake City's International Airport are working with the state's medical examiner in the investigation of the incident.

The man reportedly collapse shortly after the plane landed in Utah.

Army Reserve medic Jared Noal was on board the flight and noticed the man was having problems.

"You could tell something was wrong. I asked, 'Hey, sir, are you awake?'" Noall said to KSL-TV.

The unidentified passenger had been heard snoring loudly about 20 minutes before landing but after a few sudden movements, the passenger stopped snoring and suddenly collapsed.

Noal and other passengers rushed to his aid and the medic attempted CPR in order to revive the stranger.

"I shook him a bit, trying to see if I could get a response out of him," Noal recounted. "We checked his throat for a pulse, and it wasn't there, so we laid him down in the aisle and start CPR."

Paramedics were called to the scene and the unidentified man was pronounced dead.

Kevin MacIsaac, another passenger on the flight, said that every effort was made to save the man's life.

"They tried their very best; the family of the deceased man would be glad to know he did everything possible to revive him," Maclsaac said, as quoted by The Daily Mail.

A United spokesperson confirmed to KSL that a passenger on the flight died, but no details of a name, age, and gender were released due to privacy issues.

Passenger Noal described the unidentified person as a man in his thirties.