Five people were arrested after missiles were thrown at police during "appalling" scenes of violence following this year's Luton Carnival.
Video footage of the violence posted online showed officers using batons to break up fights in the town centre and a victim being cuffed to the ground by a hooded youth near a police van.
Bedfordshire Police said two people were taken to hospital by ambulance after the clashes, which broke out at about 8.15pm on Sunday.
Chief Superintendent David Boyle said: "It is disappointing that after a fantastic day of celebrations during Luton Carnival, we have seen a small minority of people causing ugly scenes across the town centre.
"This behaviour will absolutely not be tolerated and we have launched an investigation to ensure that all those responsible are identified and justice is brought against them."
Thanking neighbouring forces and fire and ambulance service colleagues for their support, Mr Boyle added: "The carnival itself passed peacefully and safely, as it has done for several years, and it is completely unacceptable that some people have attempted to ruin that.
"We would like to reassure the public that we are taking the events of this evening very seriously and would appeal for anyone who witnessed the disorder to contact us so that we can help bring those responsible to justice."
Hazel Simmons, leader of Luton Council, said she was appalled at the violence, which forced police to form several cordons to keep groups of youths apart.
Pledging her support to the strongest punishment possible for those involved in the violence, Ms Simmons added: "We should all be sitting back and celebrating what was a fantastic spectacle with thousands of people coming out and enjoying a wonderful carnival event in Wardown Park.
"Instead, we have to condemn the actions of a small minority of people who have shown complete and utter disrespect to the town and its people."
Anyone with information about those involved in the clashes or who filmed video footage of disorder is urged to contact police on 101.