Two boys aged 14 and 15 been arrested on suspicion of attempted murder after a 14-year-old boy was stabbed multiple times in north London.

The boy was stabbed in the stomach with a 10-inch kitchen knife on a busy street as onlookers pleaded with the attacker not to do it, a witness said.

Police were called to Fairbridge Road, Islington, shortly before 7pm on Sunday after receiving reports of an injured male. The teenager was found with a number of stab wounds and taken by air ambulance to an east London hospital.

He remained in a serious but stable condition with his family at his side late on Sunday evening.

An 11-year-old boy who was arrested on suspicion of attempted murder was de-arrested and released from custody, the Metropolitan police said. They said he was no longer a suspect.

The mayor of London, Sadiq Khan, said: “Incidents like this have a devastating impact on families and our communities and we need to send the message that they will not be tolerated. Politicians, the police and all Londoners must unite in saying it is never acceptable to carry a knife – and it does not make you safer.”

Amina Taylor, a local resident, said two men and what appeared to be two young teenagers were involved in a fight for a few minutes before a third teenager ran towards them carrying a “cumbersome” weapon.

Taylor witnessed the stabbing from the balcony outside her second floor flat overlooking the scene of the crime and said all those involved were white.

“We could all see the knife in his hand. It was that big,” the 40-year-old said. “You could hear the screams of ‘No, stop it, don’t do anything, don’t be stupid’ and he went for one of the adults first but then he was kind of swinging wildly and then he just thrust the knife into the stomach of the teenager.”

In a statement, the Met said: “At this early stage officers retain an open mind as to motive. A crime scene examination is under way near Archway tube station, and inquiries are ongoing.

Police have appealed for anyone who saw the stabbing to contact them.