"It could have been a lot more serious. Several people were struck by flying bottles."
St John Ambulance confirmed they took two people to Rotorua Hospital -- one in a serious condition and the other with moderate injuries.
Mr Murphy said the incident was a good reminder of the importance of people registering their parties so police could help ensure party organisers had the information to keep guests safe, as well as were aware of the party in case something went wrong.
People can register their parties online via the Rotorua District Council website or call the police.
"As we move into the warmer months it's a good idea for people to register their parties so police know about it. If something does go wrong like gatecrashers we have a record of who to speak to.
"We'd rather engage with them early so we can nip some of the problems in the bud."
Mr Murphy said about 12 police were needed at the party scene which he described as "fairly chaotic".
There were about 60 people attending the party, mainly in their late teens and early 20s.
However, he didn't believe this was a case of a poorly organised party.
"It was criminal gatecrashers who attempted to enter uninvited and then started throwing bottles into the crowd."
The organisers of the party said they were left shaken and scared after the incident. They said those who turned up at the party seemed to be "looking for trouble".
The woman said they rarely held parties and had been reluctant to hold this one. She said if they had one in future, they'd definitely be registering it with the council and police.
• Mr Murphy said anyone with information should phone the Rotorua police on (07) 348 0099.
