A heartwarming video has emerged of passengers singing ‘Happy Birthday’ to a flight attendant on board a US commercial flight.

The footage, captured on board a Southwest Airlines flight from Denver to San Diego late last month, shows passengers clubbing together to serenade the flight attendant.

According to the filmer, after finding out that the cabin crew member was celebrating their birthday, one passenger borrowed the cabin's loudspeaker and began the sing-a-long.

"I flew Southwest from Denver to San Diego, on January 30th, 2015, and this is what happened during my flight,” the filmer later wrote online.

"This guy decided to sing Happy Birthday to our flight attendant because Southwest is always such a fun airline to fly with, and the flight attendants are always so accommodating, friendly, and funny too!"

A heartwarming video has emerged of passengers singing ‘Happy Birthday’ to a flight attendant on board a US commercial flight.

The footage, captured on board a Southwest Airlines flight from Denver to San Diego late last month, shows passengers clubbing together to serenade the flight attendant.

According to the filmer, after finding out that the cabin crew member was celebrating their birthday, one passenger borrowed the cabin's loudspeaker and began the sing-a-long.

"I flew Southwest from Denver to San Diego, on January 30th, 2015, and this is what happened during my flight,” the filmer later wrote online.

"This guy decided to sing Happy Birthday to our flight attendant because Southwest is always such a fun airline to fly with, and the flight attendants are always so accommodating, friendly, and funny too!"