About 200 people turned up for an illegal rave in a woodland, police say.
Officers said they found one male with a broken leg and one female with a broken ankle after the party, which started in Rainford, Merseyside, at 20:00 BST on Friday.
Another female suffered burns to her legs.
Four men were arrested on suspicion of public order offences and equipment, lighting and lasers were seized.
The men were also detained on suspicion of causing a public nuisance and were taken into custody.
'An extra strain'
Current government rules restrict public gatherings to no more than six people in England due to the impact of coronavirus.
"A large number of young people were seen on the site and attempting to gain entrance from around 8pm," a Merseyside Police spokesperson said.
"Police turned away around 200 people in vehicles and on foot."
Officers said they also dealt with 12 people for drugs offences and issued 15 penalty tickets for breaching coronavirus regulations.
"A significant amount of rubbish, alcohol containers and evidence of drug misuse was located and the site," a spokesperson said.
Ch Supt Ngaire Waine added: "It is clear that the organisers and those attending care very little for public health, the community surrounding them or indeed their own safety.
"Having to deal with these sorts of unnecessary incidents puts an extra strain on both police and our partners at a time when all key workers face a huge challenge to join the national effort to beat this pandemic while continuing to protect the public."