Officers were called to the mosque near Regent’s Park just after 3 p.m. local time, and found a man in his 70s with stab injuries, London’s Metropolitan Police said in a statement.
Images and videos posted to social media appear to show officers restraining a man in a red sweater on the floor of the mosque.
Eyewitnesses told CNN there were around 100 people in the mosque at the time, and several helped pin the assailant to the ground. Some said they had seen the attacker attend the mosque in recent weeks.
One video posted online showed a knife on the floor next to the man.
“A 29-year-old man, who is believed to have been attending prayers, was arrested inside the mosque on suspicion of attempted murder,” police said in a statement.
“He has been taken into custody at a central London police station. A crime scene has been put in place. Enquiries continue.”
London mayor Sadiq Khan added: “Every Londoner is entitled to feel safe in their place of worship & I want to reassure London’s communities that acts of violence in our city will not be tolerated.”
Police are providing extra resources to the area, Khan said.
In a statement, the mosque said: “there was an Incident today at London Central Mosque where an unknown individual attacked and stabbed the muazzin (the person who makes the call to prayer) during Asr Prayer around 3 p.m.
“The attacker was apprehended by the worshipers until the police arrived and arrested him. The muazzin did not sustain any life-threatening injuries but was seriously injured and is being treated at the hospital.”
Miqdaad Versi, a spokesperson for the Muslim Council of Britain, described the attack as “extremely worrying.”
“We must have no hesitation in condemning such evil,” Mohammed Shafiq, CEO of the Ramadhan Foundation, added in a statement. “Mosques and all places of worship are sacred and should be protected.”