A 20-year-old man has died after he was stabbed during a mass brawl in Preston.
The Asian man, who has not been named, was killed during a fight involving about 40 white and Asian men and youths on the city's Callon Estate.
Several other people were injured during the disturbance, in which knives, bottles and baseball bats were used, police said.
Supt Richard Bailey, of Lancashire Police, said a number of people had been arrested over the incident.
He said: "We are treating this as a very serious incident and we are working with the local community to reassure them and they are helping us with our inquiries.
"A number of people have been arrested. However, as numerous people were in the vicinity at the time, we are asking them to contact us."
Anyone with information about the incident, which happened at about 0045 BST on Saturday, should contact detectives.