A 16-year-old Asian youth was stabbed in the arm as disturbances involving 200 people flared following attacks on cars parked at a mosque.
Police said the attacks were racially motivated, and extra officers were patrolling the Avenham area of Preston.
Bricks and concrete blocks were thrown at cars of people attending the mosque.
Chief Supt Mike Barton said: "These problems are being caused by a small group of criminals in the area intent on intimidating the local community."
The stabbed youth was not seriously injured and there were no arrests, police said.
The disturbance follows the death of an Asian student in July after a fight between up to 40 Asian and white youths nearby, which police described as a "suspected race attack".
About 100 officers were called to the Jamia Masjid mosque when disorder broke out on Sunday evening on Clarendon Street.
Ch Supt Barton said there was a growing element of criminal, anti-social behaviour in the area and those responsible needed ridding from the community.
He said: "This incident of stone throwing is an example of that, and as you can expect, people are unhappy with being victimised.
"[On Sunday] a number of cars were damaged outside the mosque and people who were worshipping inside came out to see what was going on. Not surprisingly, they have been very angry."
He said because of the large number of people on the streets, police decided to deploy more officers to offer reassurance and prevent disorder.
Patrols are being boosted and police are using video cameras to gather evidence. They are warning that people who launch reprisals will be arrested.
In July Shezan Umarji, 20, was killed on the Callon Estate, one and a half miles away from Avenham.