Six people have been reported injured in a suspected noxious substance attack at an east London shopping centre, police said.
Scotland Yard said officers were called shortly before 8pm on Saturday to the area around Stratford Centre, opposite the Westfield shopping centre, amid reports of a group of men spraying what is believed to be a noxious substance.
One man has been arrested on suspicion of causing grievous bodily harm.
London Ambulance Service paramedics and the London Fire Brigade also attended as a number of victims were reported at different locations within the centre, with the number affected believed to be six people.
A spokesman for the Metropolitan Police said the attack was not being treated as terror related.
Officers remain at the scene and a cordon is in place.
Witnesses at the scene said an argument broke out among a group of people.
A man who gave his name as Hossen, 28, a Burger King assistant manager, said he saw a victim and his friend, a known local homeless man, run into the fast food outlet bathroom "to wash acid off his face".
He said: "There were cuts around his eyes and he was trying to chuck water into them."
Inside the Burger King toilets, water could be seen all over the floor, along with toilet tissue and medical gloves.
Outside, people gathered at police cordons while victims were being treated behind a blue screen.
Many of those at the scene, kept inside the cordon by police, were visibly upset by the incident.
One said: "I can't speak now, my mate's been hurt."
Paul Gibson, assistant director of operations at London Ambulance Service, said: "We have sent a number of resources to the scene including paramedics in cars, ambulance crews, an incident response officer and our Hazardous Area Response Team.
"So far, we have treated at least five patients at the scene and taken three patients to hospital. We remain on scene."