Two so-called zombie knives and two Rambo-style blades were found at the scene of an attack on a 16-year-old boy, police have said.
Five weapons were discovered by officers following the incident on Tuesday evening in Brixton, south London - the other one being a kitchen knife.
The boy was repeatedly stabbed and is in hospital in a serious, but stable, condition.
Dame Cressida Dick, the Metropolitan Police Commissioner, said: "Last night, a 16-year-old boy, having just left home on his bike, as I understand it, was knocked off his bike, it appears, by a car, and then stabbed repeatedly in many different places.
"We recovered from the scene two Rambo knives, two Zombie knives, a kitchen knife."
Under the Offensive Weapons Act 2019, a zombie knife has either a cutting edge or a serrated edge or both, and "images or words (whether on the blade or handle) that suggest that it is to be used for the purpose of violence".
Detective Inspector Yasser Awad, who is leading the investigation, said: "This violent attack has left a teenage boy in hospital with serious injuries.
"We believe there may be people who saw what happened to him but have not yet come forward."
Police are keen to speak to anyone in the area who "heard a commotion or saw anything suspicious", as well as the driver of a white van which was on Henry Road between 6.15pm and 6.20pm.
"We believe the driver may have vital information," DI Awad said.
The incident comes as Dame Cressida warned of a rise in "certain types of crimes" as lockdown eases.
Speaking to City Hall's police and crime committee, the commissioner said that there had been "ghastly offences" at the start of this year - including "horrible homicides".
She spoke of how more than 1,000 charges had been brought against county lines operators in the 16 months since November 2019, adding that 324 lines had been closed.
Dame Cressida also told how the Met had seized 43 firearms between 7 and 18 February - including an Uzi submachine gun, a sawn-off pump action shotgun, and pistols.
"I am not suggesting that we can see a trend at the moment of violence going up," she said.
"Of course, I fully expect that there will be an increase in certain types of crimes, however well we do our job, when we do begin to ease lockdown measures."
