This is the moment two men were caught on camera throwing punches at each other in front of shocked passengers as their aeroplane prepared to take off from Narita, Japan.

Footage posted on Twitter shows air cabin crew on the All Nippon Airways (ANA) flight desperately trying to separate the pair as the plane was about to fly to Los Angeles, US.

One of the men fighting, dressed in a black T-shirt, is heard shouting to other passengers mid-brawl: "Someone help, this guy is crazy."

The other man, wearing a ripped Hawaiian shirt, and who appeared to be American, responds: "I'll kill you."

After throwing more punches, he is then led away by an air steward, with him heard shouting: "America."

The violent incident appeared to be over but, to the surprise of other passengers, the man in the red shirt was able to return and exchange more blows with his fellow traveller. The video clip ends as it shows him being knocked back with a punch to the face.

The passenger who filmed the incident, US-based photographer Corey Hour, said the fight eventually ended "when I stepped in and confronted the man in the red shirt".

"I told him to leave and squared up with him, he backed down [and] left," he wrote on Twitter.

Hour said the motive for the fight was not known, adding that at one point the man in the red shirt yelled: "You think I'm crazy? What about the government?"

The man also allegedly claimed to have been contracted by the government to carry out a hit in Las Vegas, Hour said. "Then he went rogue and started fighting civilians."

According to police and an ANA airline spokesperson, the incident happened on Monday night (1 May) just before the plane was due to depart for Los Angeles. The man in the red shirt was eventually escorted off the plane.

A 44-year-old American male passenger has since been charged with assault, according to Japan Times.

After allegedly boarding the plane drunk, he was deemed a potential safety threat and had been asked by the airline to leave the plane. The man resisted, however, and is said to have hit another passenger before leaving the plane and choking a male ANA employee.

The flight – which had already been delayed due to poor weather – finally departed an hour and 40 minutes behind schedule.

"For the record ANA staff and passengers handled the situation with grace and respect. They did the best they could to diffuse the situation," Hour tweeted.