Police were called at 11.18am to reports of a “corrosive substance attack” at Bloomsbury Place.
Emergency services rushed to the scene to find a man in his 30s had been sprayed in the face with a substance that had inflamed his eyes.
Officers believe the attack occurred during a personal robbery.
The victim was treated by paramedics and the London Fire Brigade before being taken to hospital.
There have so far been no arrests in connection with the attack.
Police have closed part of Bloomsbury Square with the junction of Bloomsbury Place.
A large cordon has been put in place outside outside a building that is listed as a hotel and services flats.
The Metropolitan Police said in a statement: “Police were called at 11:18am on Tuesday, April 13 to reports of a corrosive substance attack at Bloomsbury Place, WCI.
“Officers, London Ambulance Service and London Fire Brigade attended.
“At the scene a male, aged 30s, had been sprayed in the face with a substance that had inflamed/irritated his eyes.
“At this early stage detectives believe that the attack was sustained during a personal robbery.
“The victim was treated by medics and London Fire Brigade at the scene. We await further updates.
“There have been no arrests. A crime scene remains in place.
“Anyone who witnessed this incident or captured moving footage is asked to contact police on 101 or Tweet @MetCC quoting 2507/13APR.
“To remain 100% anonymous call the independent charity Crimestoppers on 0800 555 111 or visit Crimestoppers_uk.org.k.org.”
A London Ambulance Service spokesman said: “We were called at 11.18am today (April 13) to reports of an incident in Bloomsbury Place, WC1.
“We sent an ambulance crew, an incident response officer, and a hazardous area response team.
“A man was treated at the scene and taken to a hospital.”
This is a breaking story. More to follow…