A 16-year-old boy is in custody after two males on a moped carried out five acid attacks across London in less than 90 minutes, police said.
The teenager was arrested on suspicion of robbery and grievous bodily harm following the assaults, which the Metropolitan Police said appeared to be linked.
Two involved victims having their mopeds stolen, while one victim has been left with "life-changing" injuries after being doused on Thursday night in the east of the capital, the force added.
Labour MP Stephen Timms, who will lead an adjournment debate on acid attacks in the Commons on Monday, has called for tougher sentences for those found guilty, while Commissioner Cressida Dick revealed the Home Office is working with the Met to see if a change in the law is needed.
She branded acid attacks "completely barbaric", telling LBC: "The acid can cause horrendous injuries; the ones last night involved a series of robberies we believe are linked - I am glad to see we have arrested somebody."
The 16-year-old youth is being held at an east London police station.
London Ambulance Service said they were called to the first attack in Hackney Road at 10.16pm, while police were alerted to the night's final assault at 11.37pm.
At the start of the rampage, a 32-year-old moped rider was approached by the pair as he drove towards the Hackney Road junction with Queensbridge Road.
Two male suspects tossed a noxious substance into his face before one of them jumped on to the victim's vehicle and drove away.
One witness saw police pouring huge bottles of water over the victim just outside her flat.
Sub-editor Sarah Cobbold, 29, told the Press Association: "I had thought someone must have chucked petrol or acid on him or something because they were covering him in water, but I have never seen that reaction to an attack, I thought maybe there had been an accident."
Police said the man had been taken to an east London hospital and they were awaiting an update on his injuries.
Little more than 20 minutes later, at around 10.50pm, another victim had been sprayed with a searing liquid by the pair at the Upper Street junction with Highbury Corner in Islington.
The victim was taken to a hospital in north London.
Then at around 11.05pm, the fast-moving attackers swooped on a man in Shoreditch High Street, tossing a substance in his face.
His injuries were not life-threatening, police said.
Within 15 minutes, the attackers appeared to have struck again, launching a corrosive substance at a man in Upper Clapton Road, causing "life-changing" facial injuries.
The final assault was reported to police at 11.37pm, when another man was confronted as he sat on his moped in traffic in Chatsworth Road.
After again spraying a liquid in the victim's face, the moped was stolen and both attackers fled.
Hazardous area response units were sent by the ambulance service to four of the scenes, while the victim of the Chatsworth Road attack took himself to hospital.
The attacks come just days after John Tomlin, 25, appeared in court accused of throwing acid at aspiring model Resham Khan, 21 and her cousin Jameel Muhktar, 37.
They were left with life-changing injuries after the attack on Ms Khan's 21st birthday in Beckton, east London.
One man, who lives in the block of flats overlooking the scene of the attack in Upper Clapton Road and did not want to be named, said: "I saw the road closed for a couple of hours. It looked really scary. I saw the aftermath. I saw the motorbike on the pavement."
Asha Kaur, 26, said it was frightening to think that an attack happened so close to where she lives off the Upper Clapton Road.
The beauty therapist, who got home on Thursday night at 11pm - shortly before the attack - said: "It's just scary because I walk to work and it's just literally outside your doorstep.
"Even with my phone, you've just got to be extra cautious and hide it all away."
Ms Kaur said she has told her 22-year-old brother to be "extra careful".
A woman who lives in flats off Upper Clapton Road, who did not want to be named, said she heard shouting coming from outside, although she thought it was closer to 12.20am.
"I just saw blue flashing lights and heard a load of shouting," she said, adding that she heard someone shout "Oi, what do you think you're doing?"
She said: "I just thought it was a fight broke out because it was the time people would have been coming home from the pub.
"There was so much shouting going on. I looked out my window in case it was a woman being mugged or attacked."
Theresa May's spokeswoman said the Prime Minister viewed acid attacks as "horrific".
She told a Westminster briefing: "It is already an offence to carry acid or a corrosive substance with intent to cause harm. And anyone using it can be prosecuted for pretty serious offences including ABH and GBH.
"We are working with the police to see what more we could do.
"The Prime Minister's view is that the use of acid in this way is horrific."
Sandra Smith, 37, lives in a flat off Upper Clapton Road and said she heard a "commotion" and saw a moped parked up after the attack.
"I just heard the commotion. There wasn't anything to see by the time we got out here," she said, adding that she spotted a "black moped" with a "box on the back of it".
Ms Smith said: "It's a nice area. It's a multi-cultural area. Everyone gets on. We all mix.
"We've never faced anything like this. It's a quiet area. We never really get any problems, the odd petty crime.
"Everyone's quite shocked. An acid attack, you hear about it, but never close to home."
Outgoing Liberal Democrat leader Tim Farron said: "More needs to be done to tackle the horrific rise in acid attacks we are seeing in London and across the country.
"Acid is a potentially deadly weapon that can cause life-changing injuries, it must be treated as such.
"We need to look at how best to restrict the availability of acid and ensure those committing these horrific attacks are brought to justice.
"That should include increasing funding for community policing to gather intelligence, prevent crime and make our streets safer."
Emmanuella Stamou, 48, whose mother lives close to where the Upper Clapton Road attack happened, said: "It don't matter where you are these days. It is quite scary to be honest. Hackney quietened down but then you hear this."
She said she thinks the law needs to be tougher, adding: "If you get caught with a knife you get done for it. Now they're using acid."
Ms Stamou added: "I think the law in this country is no good anyway."
Eliezer Frischman, 28, was on Upper Clapton Road shortly after the attack when the emergency services were still at the scene.
"I understood the victim was still on the scene," he said. "I think it was him. He looked okay. He was walking around. I think he was taken in to hospital.
"I just saw his motorbike and his coat next to it and his helmet."
Mr Frischman called on police to put a stop to this sort of crime, saying: "If they don't stop it now... You see last night, there was five attacks."