A man was arrested after four women were stabbed in a Sainsbury's car park in Hampton, south west London.
One woman was left in a life-threatening condition and three others were also injured in the attack on Friday morning.
A statement from the Metropolitan Police said: "Police officers have arrested a man in Hampton after a number of women suffered knife injuries during an incident.
"Police were called at approximately 10:35hrs on Friday, 20 May, to The Avenue in Hampton, Richmond and Twickenham, following reports of a man in possession of a knife.
"Officers attended and discovered three women [ages unknown] suffering from knife wounds.
"The London Ambulance Service also attended and are providing treatment to the women. Their conditions are not thought to be life-threatening or changing at this time.
"A fourth woman who had also suffered knife wounds was subsequently located at a nearby property. She has been taken to hospital where her condition at this stage is thought to be life-threatening.
"A man in his 60s [no further details at this stage] was arrested at the scene on suspicion of attempted murder and is currently in custody at a south-west London police station.
"A TASER was deployed during his arrest; but it was not discharged.
"At this early stage, the incident is not believed to be terror-related.
"Enquiries are ongoing."
The Press Association reported a member of staff at the nearby Hampton Pub said the knife man was only targeting women in the unprovoked attack.
"He only went for the women," she said. "The man ran through and started attacking them. It didn't seem like they knew him it was completely unprovoked.
"If it had been 10 or 20 minutes earlier there would have been children there because it's right outside a primary school.
"He was caught very quickly just outside the car park. He appeared to be out of it, on drugs or crazy.
"The woman who was badly stabbed in the back made it up to the police station and raised the alarm.
"She is well-known locally and always goes shopping there all the time."
A London Ambulance Service spokesman said: "We were called at 10.38 am to reports of stabbing incidents near The Avenue, Hampton.
“We sent a single responder by car, incident response officer and advanced paramedic, and ambulance crews alongside London’s Air Ambulance.
“We treated four women at the scene for various stab wounds including to the chest, legs and back.
“We took three women as a priority by road ambulance to a major trauma centre in South London. The air ambulance took the other woman as a priority to another major trauma centre in Central London”.
A member of staff at Tangley Park Children's Centre, which backs onto the scene of the stabbing, said: "We kept all the children safe and kept them in the building until we knew it was safe.
"It's just such a shock - our parents and children could have been walking to their cars at that time.
"Our sympathies go out to everyone who was hurt and we are really glad none of our families were involved."