Police are investigating a fight at a gatecrashed party in Sydney's west that left a man in hospital - the second such incident in as many days.
An 18-year-old man was struck in the head by a glass bottle at an 18th birthday party in Seven Hills.
Acting Superintendent Bob Fitzgerald says the party was gatecrashed by about 20 uninvited guests and a fight broke out.
"It's my understanding at this stage that the person who's thrown the glass bottle were part of the gatecrashers," he said.
He says his officers were surprised to be called to the party, given it was held at a community centre.
"If anyone wants to hold a party at any of the Blacktown Council community centres, there's a joint process with Blacktown Council," he said.
"We do a risk assessment [and] provide them with information on how to hold a safe party.
"This one occurred a little early in the evening - 9.15pm, which, in summer, is a little early for this sort of incident."
The uninvited guests left the party a short time later. The victim received stitches in hospital and has since returned home.
The incident comes just one day after a 17-year-old boy was at another 18th birthday party on Sydney's northern beaches.
The 17-year-old underwent surgery and remains in a critical condition at the Royal North Shore Hospital.