A Golders Green synagogue was sealed off to the public on Sunday after a man carried out a pepper spray attack inside the building.
Police and fire brigade officers arrived at the Beis Hamedrash Beis Shmuel shul on Golders Green Road at around 1pm and began examining CCTV footage of the incident.
A male is said to have fled the scene after spraying pepper spray inside the building, which is now being treated as a crime scene.
There were claims that the incident took place while prayers were being said.
According to the Shomrim North West London Twitter feed the incident is not believed to be racially motivated.
A spokesperson for Shomrim North West London said: “Shomrim were called today at 12:55pm that a male suspect had sprayed what was thought to be pepper spray in the synagogue in Golders Green.
"The caller explained the suspect had fled immediately from the scene using a vehicle. Police and Hatzola ambulance service were called immediately to assist a victim who was sprayed in the face.
"The Synagogue was immediately evacuated by Shomrim and Hatzola volunteers. Barnet Police sealed off the Synagogue and declared the premises an active crime scene. Shomrim volunteers are assisting Barnet Police with the enquiries and the gathering of witness statements and CCTV footage."
Police and fire officers left the scene later on Sunday afternoon and the building was reopened for services.