Police were called to John Street, Bradford, shortly after 5.45am this morning (Sun Oct 10) and found two 19-year-old men with stab wounds.
West Yorkshire Police said one of the men died a short time later.
The other man is in hospital in a critical but stable condition.
A youth aged 16 and a 26-year-old man have been arrested on suspicion of murder and attempted murder and are currently in custody.
Detective Chief Inspector Marc Bowes, of the Homicide and Major Enquiry Team, said: "One young man has unfortunately lost his life and another is continuing to fight for his.
"This is an absolutely devastating incident and a significant police operation and investigation is underway to identify and arrest those responsible.
"As a result of our enquiries, two males have been arrested and we are continuing to gather evidence in relation to this tragic incident.
"This has happened in a prominent location in Bradford city centre and, while the area is generally quieter at the time of the day that this incident has happened, there will have been people around.
"Our understanding from initial calls to the police is that there was a large group fighting and a number of these people will be significant witnesses and we would urge them to make themselves known.
"I ask that anyone with information, however insignificant it may seem in itself, to please make contact as soon as possible as it could be significant to our enquiries."
Anyone with information is asked to contact the Homicide and Major Enquiry Team by calling 101, or using the 101 Live Chat facility on the West Yorkshire Police website, quoting crime reference 13210516983.
Information can also be passed to independent charity Crimestoppers anonymously on 0800 555 111.