A man has been bashed to death in front of passengers at Sydney Airport.

Witnesses say a group of up to 20 men attacked the man in the Qantas domestic terminal earlier this afternoon.

They say the fighting began near the departure and arrivals gate before moving to the check in area.

One witness, Phil Crew, says the group closed in on the victim, using the metal bollards in the check in area as weapons.

"It looked like two people fighting at first, and then all of a sudden a whole rush of guys came through the crowd, picked up the poles and just started smacking this guy in the head with the poles," he said.

Mr Cruz says the group of men then fled, escaping in taxis.

"They started grabbing the metal poles that break up the check in area and swinging them almost like swords at each other heads," said another witness, Naomi.

"Then one man with a metal pole, another man was on the ground, and [he] started smashing his head."

Nurse Karen-Anne Whyte from NSW's far south coast, witnessed the attack and came to the victim's aid.

"A couple of men were hitting him with one of those really large bollard things and he fell," she said.

"I work in emergency departments and Moruya and Batemans Bay hospitals so I just commenced giving him CPR because he had a massive head injury."

The 28-year-old victim was taken to Prince of Wales Hospital but police have since confirmed he is dead.

Detective Inspector Peter Williams told a news conference that police were investigating outlaw motorcycle gangs over the incident.

He described the attack as "gruesome" and the perpetrators as "groups of cowards" purporting to be tough.

He said police were not ruling out a connection between the incident and a series of drive-by shootings in the western Sydney suburb of Auburn overnight.