One officer was bitten after hundreds of people “swarmed” the streets of Basford in Nottingham, with some seen defecating in public.
People living nearby said the party was going on for at least seven hours on Saturday afternoon and evening.
The stabbing is being treated as attempted murder, police said.
One woman living nearby said she first heard the party at about 3pm.
“It became quickly clear people were arriving by car travelling into the area, parking in surrounding streets, [and we] felt literally hundreds of people swarming around our streets,” she said.
‘Community needs answers’
“People getting to the party were jumping over a large fence at the bottom of the cul-de-sac. People were drinking in the street and it was still going on at 9pm. We saw people defecating in the street.”
“We are a community that needs answers today as to why people thought it was OK to drive into our community, create anti-social behaviour and why was it not deescalated,” she said.
Nottinghamshire Police said the 18-year-old man was stabbed at about 10pm, and he was taken to hospital with serious injuries.
The force said the party was advertised on social media and organised by a group suspected to be living in Bramble Close.
They said the gathering was initially contained but more people arrived as the evening went on, including some who travelled from outside Nottinghamshire.
Some broke through nearby gardens in an attempt to get to the party, officers said. Police dogs, a police drone and the police helicopter were all deployed.
Supt Mat Healey said it was a “brutal stabbing” in the midst of a “mob of people”.
“Covid-19 regulations prohibit large gatherings, as we are still in the grip of the pandemic,” he added.
He said it was “appalling” for officers to come under attack as they gave first aid, and three of them were injured.
Police made several arrests, including a 21-year-old man on suspicion of possession of a knife.
A 22-year-old man was arrested for having two knives in his possession, and also on suspicion of assaulting the officer arresting him.