Updated | Man charged under 'coward punch' laws over death of security guard at Sutherland hotel

A security guard "just going about his business" has died outside the Royal Hotel at Sutherland after allegedly being punched in the head by a patron, who had been requested to leave the premises.

Police have charged a 31-year-old man with assault occasioning death under "coward punch" laws.

The family of the security guard, who was believed to be in his 30s, are overseas and have been notified by police.

A police statement said emergency services were called to the hotel about 2am today (Sunday).

Police had found a man unconscious outside the hotel. They had performed CPR before NSW Ambulance paramedics arrived; however, he died at the scene.

"Police were told the security guard was allegedly punched to the head by a patron following an altercation; it's alleged the patron had been requested to leave the hotel prior to the assault," the statement said.

Sutherland shire police commander Superintendent Craig Middleton told a media conference it was a "terrible" outcome.

"The security guard is just going about his business, and there are patrons in there having a good time," he said.

"A security guard has ended up losing his life, it's just a tragedy all round, for the families involved, the people at the hotel, the emergency services - there are no winners in this situation."

Supt Middleton said the reasons for the altercation were still being investigated, "but I can confirm the 31-year-old male had been asked to leave the premises previously".

Supt Middleton said the altercation was seen by a number of witnesses and captured on CCTV.

No weapons had been involved.

Asked if it was a "coward punch" situation, Supt Middleton replied, "He was charged with that legislation yes".

Supt Middleton said, from what he had been told, the man who had been charged came from outside Sutherland Shire.

He has been refused bail and is due to appear before Sutherland Local Court tomorrow (Monday).