A suspect arrested over a stabbing rampage which left one man dead and five people seriously injured today has a "history of mental illness", police said.
Chief Superintendent Simon O'Brien said the attacks in north London appeared to have been "a completely random cross-section".
The victims were both male and female and of different ethnicities, he said.
Detectives were keeping an open mind about links to the fatal stabbing on Wednesday of shopkeeper Mahmut Fahri, which would be a "major line of inquiry".
The male suspect was arrested in a red Hyundai by unarmed officers this morning.
The suspect was arrested after he pulled up in the car outside his home in Haringey, north London.
He did not put up a struggle and police recovered a knife. There have been no attacks since he was held.
Mr O'Brien said his officers would be investigating whether there was a link between the random attacks and the killing of Turkish Cypriot shopkeeper Mr Fahri at his off licence in the Green Lanes area on Wednesday.
He said: "It will be a major line of inquiry."
He added: "This morning we are dealing with the tragic death of a man who has been stabbed.
"The Metropolitan Police and my heart and prayers go out to his family.
"At 8.20am we were called to the first stabbing and that man went to hospital where he is in a serious but stable condition.
"Forty-five minutes later other calls came in to other stabbings in the area. One of those people stabbed has died.
"The stabbings were random and there appears to be no link between the victims. They were also a cross-section in terms of ethnicity.
"It has been a terrible morning and the investigation goes on."
Around 60 or 70 officers are working on the case and forensic teams are at each stabbing scene.
He said police had received information about the suspect and had gone to his house. They were waiting for him when he pulled up in the car.
Detectives currently think only one person committed all the crimes, although Mr O'Brien added: "We are keeping an open mind as to whether others were involved."
Police said the 30-year-old man was arrested in Tottenham at 9.24am.
He was approached in the street by local unarmed officers after the suspect's details were circulated over the police radio.
The man who died was aged 40 and was found in Advent Way, Edmonton. A post mortem examination is due to be held.
Scotland Yard said a 29-year-old stabbed in Edmonton Green was now in a stable condition.
A man found stabbed in Gladstone Avenue was in a serious condition and a 30-year-old woman found injured in Compton Crescent was in a critical condition.
A man aged 30 who was found injured in Ecclesbourne Gardens at 9.11am was in a life-threatening condition.
At 10.45am, a 76-year-old man arrived at North Middlesex Hospital in Edmonton with stab wounds.
It appeared he was attacked in Empire Avenue and had walked from there to the hospital. He was in a serious condition.
An incident room has opened at Edmonton police station on 020 8345 1585.
The man who died had been taken to Whipps Cross hospital in Leytonstone while the other five victims were being treated at North Middlesex hospital. Two of them were in surgery.
The suspect - described as Turkish or Middle Eastern - was arrested following the attacks carried out using a car around the Green Lanes area.
Mr Fahri was knifed to death as he chased two thieves who stole bottles of spirits from his grocery store in Wood Green, north London.
Enfield Council leader Michael Rye said today's stabbings were the latest in a series of incidents in the borough which left residents "increasingly concerned".
He said: "I am shocked and appalled that this could happen in Enfield. My thoughts are with the victims and their families.
"This is the latest in a series of unrelated violent incidents in the borough and I know residents are growing increasingly concerned about crime.
"We are working with the police and trust that they will ensure the capture of the perpetrators of these terrible crimes and do all they can to respond to local people's concerns."
Dr Yasmin Drabu, medical director of North Middlesex Hospital, said the five patients were admitted to the hospital at about 9am.
"Three of them are still in theatre and one has been transferred to the heart hospital," she said.
"One has not gone to theatre and is being observed in our high dependency unit."
She said the patients had sustained "a number of knife wounds" but she could not go into details about their injuries.
Dr Drabu said the three people in surgery were expected to remain there for at least another hour. The patient transferred to the heart hospital needed specialist surgery.
She said the condition of the three undergoing surgery was thought to be stable, but it would not be clear until they had come out of theatre.
Dr Drabu said the fourth man at the hospital in the high dependency unit was in a stable condition.
Describing the nature of the injuries, she said: "The stabbings were all over the place in various parts of the body.
"They did have multiple stab wounds, one patient certainly had multiple stab wounds."
The North Middlesex A&E department is the fifth largest in London and dealt with 130,000 cases last year.
Describing the events of today, Dr Drabu said: "It is not a pleasant situation at all, but unfortunately it is this sort of thing that we have to work with - not as routine, but we are prepared for this."
She said all three operating theatres were being used to treat the patients, involving at least 20 theatre staff.
When the hospital was first alerted to the incident, they expected three patients, which quickly rose to five. Dr Drabu said at that stage they feared there could have been more.
A spokeswoman for the hospital said that they had alerted nearby local hospitals to this major incident and were diverting other ambulances there.
She said: "This is standard practice, we started to back up and received immediate assistance from Chase Farm which is about four-and-a-half miles north from here."
Ambulances were diverted to the other hospital, but North Middlesex's A&E has now returned to normal.
Detectives have contacted Barnet, Enfield and Haringey NHS Mental Health Trust where staff were checking the suspect's name against their computer records.
The Trust is trying to establish whether the suspect was a patient or ex-patient at one of its centres.
Hundreds of police officers are now working on the case.
Mr O'Brien said: "It's very difficult to know what prompted this. The first victim was a man who was walking to the station to go to work. He had just left his girlfriend when he was stabbed a couple of times in the back. He thought he had been punched and carried on.
"The calls then started coming in thick and fast and we realised we were probably dealing with the same guy stabbing people."
He said the spate of stabbings had been classified as a "super critical" incident.
Mr O'Brien, the Borough Commander of Enfield, said: "We had a full uniformed response and officers from the Murder Squad and forensics and help from officers in Haringey and Edmonton.
"It was a very dynamic situation and it was very difficult to know where the next one was going to happen or what was going to happen in the next few minutes.
"He was coming out of the vehicle, picking people at random, male and female, some were cycling, some were walking and he stabbed them before getting back into his car.
"It's horrendous and I don't know what the motivation is.
"We know he is about 30-ish and a Turkish man but we have no indication at the moment that he has a criminal past."
He said victims had been stabbed one or two times each.
"Some of them carried on walking thinking they had been punched.
"One of the victims was a woman cyclist who thought she had been punched and carried on cycling.
"Finally we got a few calls with registration numbers for the car and we went to an address.
"Officers had just turned up when the suspect arrived in his car."
The suspect was arrested by unarmed officers and had blood on his clothes and inside the car.
Mr O'Brien said the attacks happened over a five or six square mile area.
The final victim discovered was a man in his 70s who walked into hospital having been stabbed.
