An Irishman has been charged after punching his brother, who is now in critical condition in a Sydney hospital after a trip of a lifetime went disastrously wrong.

Patrick Lyttle, 32, is said to be in critical condition at King’s Cross Hospital in Sydney after he was reportedly punched by his brother Barry outside Bayswater Road in Kings Cross last week, the Irish Independent reports.

Barry had just arrived in Sydney with his father from Belfast to visit Patrick. The two seemed very close according to friends and Facebook comments they made to each other.

After a meal in a restaurant their father went back to the hotel while his sons went to a nearby bar.

Soon afterwards an altercation broke out. Eyewitnesses say Patrick pushed Barry who punched Patrick once. Patrick fell and hit the sidewalk hard.

He sustained serious head injuries after the single punch. 

Barry Lyttle, 33, appeared in court on January 2 at Parramatta Bail Court, where he did not request bail. According to Australian reports, when the victim was named as his brother, Lyttle began to cry. 

According to New South Wales police, the brothers, Patrick had moved to Australia in June and Barry and his father had come to visit.

Kings Cross Police Superintendent Michael Fitzgerald said the man's father has set up a vigil by his injured son's hospital bed.

“The pain in his eyes, you could not describe,” Fitzgerald said at a press conference. “This is a tragedy. We have a father who is facing the reality of one son facing serious criminal charges, another son fighting for his life.”

The court heard that alcohol "seems to have played a part" in the assault. 

"From what I'm told, we won't know anything for at least 24 to 48 hours. They'll release pressure on the brain,” he said.

Police are continuing to investigate the incident.