Five attacks in east London which involved acid being thrown in peoples' faces from the back of a moped are being investigated by the Metropolitan police.
The attacks all happened within 90 minutes in Hackney and Stoke Newington on Thursday night and are being treated as linked.
The victims were taken to hospital, with one of them suffering what has been described as "life-changing injuries".
A male in his teens has been arrested on suspicion of grievous bodily harm and robbery. He is currently in custody at an east London police station.
One 32-year-old man on a moped was left with facial injuries after a moped, with two male riders, pulled up alongside him in Hackney about 10.30pm.
The pair threw a corrosive substance in the victim's face, say police, with one stealing his moped and the other driving away on the vehicle they arrived on.
Following this incident, at 11.05pm, a corrosive substance was reported to have been thrown in the face of a person by two men on a moped in Shoreditch High Street.
At 11.18pm police received reports of a robbery in Cazenove Rd, Stoke Newington, where a corrosive substance had been thrown.
In a fourth incident in Clapton at about 11.39pm, a man on a moped was in traffic when two men on a moped pulled up alongside him and sprayed liquid in his face, before stealing his vehicle.
Following the incidents in Hackney, officers were made aware of a similar attack reported in Islington. At 10.49pm a man was reported to have had a corrosive substance thrown in his face by two males on a moped in Upper Street junction with Highbury Corner.
The Met said enquiries were ongoing.