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, police said.
The incident was not being treated as terror-related, a police spokesman said.
The attacks occurred near the Stratford Centre, in Stratford, police said. Earlier they had said the incident took place around the bigger Westfield shopping centre which is nearby after an 'altercation' between two groups of men.
'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 8pm (1900 GMT), it said.
Chief superintendent Ade Adelekan said: 'I would like to be very clear concerning this incident.
'What initially may have been perceived as a number of random attacks has, on closer inspection, been found to be one incident involving two groups of males.'
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.