A man who flew across the globe for a birthday surprise has been shot dead by his wife's father after leaping "out of the shadows" to greet him.

Christopher Bergan, 37, flew into the US from Norway on Tuesday to wish his father-in-law Richard Dennis, 61, happy birthday.

But the trip turned to tragedy when Bergan arrived unannounced at Dennis's Gulf Breeze home in the city of Pensacola, Florida around 11.30pm.

According to police, Bergan knocked on the back door of his father-in-law's house, then hid behind bushes.

When Dennis answered, Bergan leapt "out of the shadows" while making growling noises, police said.

Dennis responded by firing one round from his .380 semi-automatic firearm, hitting his son-in-law in the heart and instantly killing him.

"He was totally startled," Santa Rosa County Sheriff Bob Johnson said of the shooter.

Authorities described the incident as a sad case of mistaken identity.

Earlier that evening, Dennis had an argument with another relative because that person had come by the home and loudly banged on his front door.

When he heard more knocking about an hour later, Dennis reportedly believed it was the same relative and opened the door while armed.

"So [Dennis] turns on the back porch light, he steps out and Mr Bergan jumps out of the shadows, scaring Mr Dennis," Johnson said.

"I'm not going to second-guess Dennis for what he did. Here he is, he had just had a confrontation at the front of his house.

"Couple hours later, someone is banging on his back door, and it's a fenced yard.

"And then someone jumps out of the bushes.

"You can't really say anything against Mr Dennis for doing what he did.

"I think it was just a horrible accident, that should never have happened."

Bergan's friend, who had driven him from the airport, also witnessed the incident.

"They were working on him when our officers got there, and our officers got there pretty quick," Johnson said.

Bergan had previously lived in Florida before returning to Norway, where he lived with Dennis's daughter and their young son.

Speaking at a news conference on Thursday, the sheriff told reporters Dennis would not be charged over the incident.

"Our investigation has revealed that this was totally accidental, it was a really sad occurrence, and that no charges are warranted in this case," Johnson said.

Amber Roland, a lawyer with the State Attorney's Office, said authorities had examined the scene of the tragedy.

"We were able to view the evidence," she said.

"We were present on scene when detectives interviewed the witnesses.

"Everything's consistent.

"We determined that [this was a] tragic accident."