The party had been for the victim's girlfriend, he said.
The vehicle and driver allegedly involved left the scene immediately after the incident, according to police. The Herald understands the people in the car were known to those at the party.
However, a friend of the alleged driver has commented on social media that reports of it being a hit-and-run are wrong.
"He didn't flee the scene. That story's all s***," he posted. He also claimed it was an accident and that the driver was not speeding.
The victim was airlifted to Waikato Hospital, where he remains in a serious but stable condition in the High Dependency Unit, a Waikato DHB spokesperson confirmed.
Residents in the Waikato town were shocked to wake up to the news that someone had been injured after a hit-and-run on the usually quiet street and expressed their disbelief on social media.
Police closed the road about 2.30am on Sunday and yellow spray paint lines remain on the road, marking out the scene.
Skid marks were etched into the road and it was littered with broken glass and empty bourbon and coke cans.
Otorohanga District Council Kawhia/Tihiroa ward councillor Kit Jeffries said the "unfortunate incident" happened at the end of his gate just before 1am. He declined to comment further out of respect for his neighbours.
A police media spokesperson confirmed they were called shortly before 1am after a person was struck by a vehicle on Rosamond Terrace.
Inquiries are ongoing and no charges have been laid at this stage. Police had spoken to one person who is assisting with inquiries, the spokesperson said.
A St John spokesperson said they received a call about a car vs pedestrian at 12.56am and sent a first response unit, a doctor, an ambulance and a rescue helicopter.
The patient was assessed and treated at the scene before being transported in a critical condition to Waikato Hospital in the early hours of Sunday.
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