An American airline has issued an apology after a mix-up resulted in a terrifying moment for a 6-year-old boy.

Multiple United States media outlets have reported the young boy named Casper was scheduled to fly on Spirit Airlines from Philadelphia to Fort Myers, Florida on December 21.

However, a mix-up saw him fly more than 260km away landing in Orlando, while his bags arrived in Fort Meyers.

Speaking to Wink News, the boy’s grandmother, Maria Ramos, said she first knew something was wrong when she was informed by the airline that he had missed his initial flight.

“They told me, ‘No, he’s not on this flight. He missed his flight.’ I said, ‘No, he could not miss his flight because I have the check-in tag,” she told the outlet adding she was so frantic by the news, that she ran onto the plane.

“I ran inside the plane to the flight attendant and I asked her, ‘where’s my grandson? He was handed over to you at Philadelphia’. She said, ‘No, I had no kids with me’.”

Spirit Airlines flew a child 260km on the wrong flight to see his family. Picture: Joe Raedle/Getty Images

Soon afterwards, Casper rang Ramos to tell her that he had landed in Orlando.

Shocked by the situation, Romas demanded answers from the airline and called to find out how it happened in the first place: “I want them to call me. Let me know how my grandson ended up in Orlando. How did that happen? Did they get him off the plane?” she told the news outlet.

Speaking to Business Insider, a representative for Spirit Airlines confirmed there had been an unfortunate mix-up and that their team had placed the child accidentally on the wrong flight.

“The child was always under the care and supervision of a Spirit team member, and as soon as we discovered the error, we took immediate steps to communicate with the family and reconnect them,” the statement read.

The airline said an internal investigation was underway and apologised to the family for the concerning turn of events.

“We take the safety and responsibility of transporting all of our guests seriously and are conducting an internal investigation. We apologise to the family for this experience.”

It is unclear when the young boy was reunited with his family and whether the airline offered any compensation.