The violence started when three men tried to enter a house in Grosvenor Road, Highbury, police said. A fight spilt out on to the street, and the victim was killed by a stab wound to the heart.
Police called to the incident were confronted by a 50-strong mob, throwing bottles and glass. The police said that it took two vans of riot control officers to restore order.
The dead man came from the King's Cross area. He is not being named until next of kin have been informed.
Two weapons were found at the scene, but the police have released no details. Six men were arrested in connection with public-order offences and later released on police bail.
Last night six people were helping with police inquiries.
Stephen and Anthony Perkins, twin brothers aged 29, from Wolverhampton, were respectively 'critical' and 'comfortable' in the Royal United Hospital, Bath, yesterday, after being stabbed during an incident at the perimeter fence of the Glastonbury pop festival on Saturday.
Police said the brothers were stabbed during a confrontation with several men, and that they are treating the incident as attempted murder. The police would like to speak to a heavily-built Afro-Caribbean, about five foot five inches tall, who tried to calm the situation.
At Holyhead, in Anglesey, Gwynedd, police were outnumbered when they were called to a street disturbance involving nearly 80 people. Reinforcements had to be brought in. Several police officers sustained slight injuries.