Six people were believed to have been injured on Saturday after a group of males reportedly sprayed a noxious substance in a number of attacks in an area around a shopping centre in east London, the police said.
The incident was not being treated as terror-related, a police spokesman said.
The attacks occurred near the Stratford Centre, in Stratford, the police said. Earlier they had said the incident took place around the bigger Westfield shopping centre which is nearby.
"A number of people have been reported injured at different locations — believed to be six people. We await further details," London's Metropolitan Police said in a statement.
One male was arrested on suspicion of causing grievous bodily harm, the statement said.
The incident occurred around 1900 GMT, it said.
Photographs posted online showed police officers crouching over an apparent victim of the attack as they treated him.
The number of acid attacks has increased in Britain in recent years, linked to robberies and gang-related violence.
The government said in July it would look at tougher punishments for people who attack others using acid.
