Scotland Yard is investigating suspected acid attacks on four people in London on Thursday night.
Within 15 minutes the attackers appear to have struck again, launching the corrosive substance at a man in Stoke Newington, causing "life-changing" injuries.
The assaults appeared to be linked and two involved victims having their mopeds stolen, they added.
The number of injured has not been confirmed, but victims have been taken to hospital.
In another, a similar substance was thrown in the face of a person on Shoreditch High Street in one of East London's most popular districts.
Four attacks took place in east London, and one in north London Twenty minutes later, at 10.50pm, another victim was sprayed with liquid on the Upper Street junction with Highbury Corner, Islington.More news: Donald Trump and President Macron meet in Paris for Bastille Day events
His injuries are not life-threatening, police said.
In one instance, the attackers - who were reportedly on mopeds - pulled up alongside a 32-year-old man who was also on a scooter, doused him in a corrosive substance and stole his vehicle.
A male teen has been arrested on suspicion of grievous bodily harm and robbery and is now being held in custody at an east London police station.
After again spraying the liquid in a victim's face, the moped was stolen and both attackers fled.
Enquiries are ongoing and officers are trying to trace the suspects.
Did you witness any of the attacks last night in London?