A 33-year-old Irish man has been remanded in custody in Sydney after he allegedly punched his younger brother in the head, leaving him in a critical condition.

Barry Lyttle from Antrim appeared in court in Sydney this morning charged with recklessly causing grievous bodily harm.

He reportedly punched his 31-year-old brother Patrick Lyttle in the head following an argument, causing him to fall to the ground.

It is believed Barry Lyttle and and his father - from Co Antrim - were visiting the victim Patrick Lyttle, who had been travelling around Australia for several months.

They had only been in the country three days when the incident happened along Bayswater Road, Kings Cross in Sydney at about 3am local time.

Kings Cross detective superintendent Michael Fitzgerald said the three family members had gone out for dinner before their father went home - and the brothers went to a bar.

Superintendent Fitzgerald said the pair got into an argument outside the club before it became physical.

One brother had pushed the other and the other reacted by punching him once in the head, causing him to fall to the ground.

Patrick was treated by paramedics before being rushed to hospital, where he underwent emergency surgery.

Barry Lyttle wept as he appeared via video link at Parramatta Bail Court this morning, as the magistrate outlined the charges.

He was remanded in custody and will reappear in court on Monday.

Both brothers are aged in their 30s.

Superintendent Fitzgerald said the older brother had been breath tested and recorded a low-range blood alcohol reading, describing the incident as a family tragedy.

Originally posted at 9.33am