A night out in Sydney’s east has ended in a bloody fight with one man knocked unconscious and another arrested.

The brawl lasted just a few seconds but police say it could now have lifelong consequences.

WATCH THE VIDEO ABOVE: Coogee street brawl leaves man unconscious

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On Saturday night in Coogee, a hug turned into a slap, then a scuffle on the street before one sickening punch laid a 41-year-old man out.

As witnesses rushed to help, they realised the man was unconscious and bleeding from the back of his skull.

Police and paramedics were called and he was taken to emergency at Prince of Wales Hospital in a serious condition.

“It’s just a horrible thing to see. It’s very violent,” worker Ava Coleman said.

Authorities say what happened is another example of how quickly things can go wrong when punches are thrown.

One man was left with serious injuries, while the other now faces serious charges.

Rangi Moore, 26, has been charged with assault occasioning actual bodily harm.

The engineer was granted bail late Sunday afternoon on a curfew and banned from touching drugs or alcohol.

His lawyer argued he was acting in self-defence.

The 41-year-old man is expected to recover. It’s unclear if he too could also face charges.