Two people were rushed to hospital with facial injuries after a "corrosive substance" was allegedly thrown at them near London's King's Cross station.
Police were called out to reports of two groups of people fighting, but they had dispersed by the time officers arrived at the scene.
"Two men were later found nearby with facial injuries reported to have been caused by a corrosive substance," a spokesperson for the Metropolitan Police said.
The did not elaborate on their condition.
Social media users posted photos online of fire engines and ambulances at the scene.
London Ambulance Service meanwhile, said: "We sent an ambulance crew and our hazardous area response team (HART) to the scene. We treated two people and took them both to hospital as a priority."
No arrests have yet been made and enquiries into the attack continue.
