A manhunt is underway and the public have been warned to be on their guard after four people were stabbed in 15 hours within a quarter of a mile radius.
A knifeman approached all of the people from behind in what police said were random attacks but not linked to terrorism.
The first incident saw a woman aged 45 stabbed in the back on Aberdeen Road, near the busy North Circular in Edmonton yesterday evening around 7pm.
The victim, 45, was taken to an east London hospital where she remains in a critical condition.
In a second incident, just after midnight and less than a quarter of a mile away, a man was stabbed repeatedly in Park Avenue.
His condition is not life threatening.
A man, 23, was knifed in Silver Street, near Seven Sisters station in the third incident, on Sunday at 3.55am.
He remains in hospital in a stable condition.
And the latest victim was stabbed in Brettenham Road a few streets away from the second victim, at 9.43am, suffering potentially life-changing injuries.
A man was arrested on suspicion of GBH at 10.53am in Fore Street and enquiries continue.
A/DCI Stuart Smillie from North Area Command said: “Police are treating the four stabbing related incidents as potentially linked.
“The four victims are all from different backgrounds and appear to have been selected at random due to them being alone and vulnerable.
“There is nothing to suggest this incident is terror related.
“We are working on the hypothesis that the single male suspect is acting alone and mental health issues may be a factor.
“All of the people he has targeted have been walking alone and he has approached from behind without warning.
“His description has been circulated to all officers in North Area who are carrying out patrols, CCTV footage enquiries and policing busy areas around where the incidents took place, particularly where he was last seen where police arrived four minutes after the call to police was made.
“A picture of this suspect will be circulated as soon as one is retrieved.
“My advice to the public in the area where these incidents took place stay vigilant, beware of your surroundings and call 999 if you see anyone matching the suspects description behaving suspiciously.”
Scotland Yard added: “Detectives are appealing for information and urging the public to stay vigilant following a series of stabbings in the Edmonton area.
“Urgent enquiries are underway to trace the single male suspect who is described as a black man, approximately 6ft 3ins tall, of skinny build and wearing dark clothing, possibly a hooded top.
“There is a lot of police activity underway to catch this suspect.
“Extra resources have been called upon and are on the streets now working to keep the public safe and catch the individual responsible.”
Members of the public who have information about this suspect or have spotted someone acting suspiciously who matches his description are advised to call police on 999 and not to approach the man.