An American national charged with the killing of an Australian man during a fight at a Thai bar claims he acted in self defence in coming to the aid of a Thai woman being assaulted.

The American, Jose Polanco, 44, surrendered voluntarily to Thai police after Victorian man Benjamin Robb, 43, died in hospital from injuries sustained in the fight in the seaside resort of Pattaya last Friday.

Thai police said Polanco said he intervened as Robb was allegedly assaulting a Thai woman, Roong-arun Sangsuwan, at the bar, called the Ruby Club.

Polanco claims Robb was arguing with Roong-arun before he grabbed the woman by the neck and lifted her off the ground, turning her face blue.

Reports said Polanco then punched Robb in the face and the Australian fell to the ground.

A statement released by the bar said the fight had lasted less than one minute.

Police and paramedics arrived at the bar soon after and Robb was transported to the nearby Pattaya Memorial Hospital. But the Australian died from head injuries in the early hours of Saturday morning.

The American initially fled the scene but later turned himself over to Thai Police. Eyewitnesses said both men had been drinking heavily in the afternoon and appeared intoxicated when the fighting broke out.

Earlier reports said Robb had also been set upon by several individuals who assaulted him with kicks to the head.

Thai police initially charged Polanco with injury to others causing death, which carries a jail sentence of three to 15 years.

Polanco did not apply for bail and will remain in the police lockup until an initial hearing in about 10 days.

The Australian Department of Foreign Affairs and Trade (DFAT) is offering support to the Robb family.

-AAP