Two men have been taken to hospital with facial injuries after a “corrosive substance” was thrown at them near Kings Cross station.
Police were called at 13:33 GMT to an altercation between two groups of men on Argyle Square, Bloomsbury.
The groups had left the location before officers and 10 firefighters arrived at the scene, police said.
Two men were later found nearby with facial injuries. No arrests have been made.
It comes after a 19-year-old boy was hurt when a “noxious substance” was thrown at his face near Romford station on Monday.
People have taken to Twitter to warn others about the attack.