The 17-year-old boy was taken to hospital with multiple stab wounds after officers were called to Kingsway Recreation Ground shortly after 6.30pm on Friday.
The victim has not yet been formally identified. His family are being supported by specially trained officers.
Police said one teenage boy has been arrested on suspicion of violent disorder in connection with the incident and is being questioned in police custody.
A second teenager arrested on suspicion of violent disorder remains in hospital with serious injuries.
A murder investigation has been launched, with detectives from the Bedfordshire, Cambridgeshire and Hertfordshire Major Crime Unit appealing for witnesses and anyone with information to come forward.
Detective Chief Inspector Nick Gardener said: “Horrific violence in Luton has sadly cost a teenage boy his life today.
“Our thoughts are first and foremost with the loved ones of the boy who lost his life in such tragic circumstances.
“Incidents such as this have a significant impact on our communities. There is currently an increased police presence in the area, and high visibility patrols will continue.”
He added: “I would urge anyone who witnessed what happened, or who has any information, to come forward and speak to police to help us bring those responsible to justice.
“We are aware that images and videos are circulating on social media. Please refrain from sharing any such footage and instead contact police. Not only is this material distressing for the family, but it could also form part of vital evidence in our investigation.”
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