A man has been arrested on suspicion of causing grievous bodily harm and assault on police after allegedly attacking two officers outside Buckingham Palace.
Reports emerging from the scene in central London say that the man had been carrying a sword before his arrest.
London's Metropolitan Police (MET) released a statement saying that two officers were injured when restraining the suspect.
The statement said: "The man [no further details] was stopped this evening, Friday (25 August) at approximately 20:35 hours by officers at the Mall outside Buckingham Palace in possession of knife.
"During the course of detaining him, two male police officers suffered minor injuries to their arm."
The force added that no other persons were injured at the scene and enquiries are ongoing.
Eye witnesses said that the man had been carrying a machete before he was overpowered by police.
Pictures circulating on social media show the area around the palace on lockdown with a cordon and a heavy police presence remaining whilst the investigation continues.
Witness Amir Jan Malik wrote on Twitter: "Being directed away from Buckingham Palace now as Police corden [sic] it off. No entry allowed in towards palace."
He added: "Stuck outside Buckingham palace with many armed police officers. Heavy rifles on display traffic at a halt."
It was reported that the Queen was not in residence when the attack outside the palace happened, as she was in Balmoral Castle, her holiday home in Scotland.
The London Ambulance Service were called and treated the injured officers who have not been taken to hospital, the Met said.
So far there is no indication that the arrest was terror related.
The London attack happened just hours after a man was fatally shot in Brussels after attacking two soldiers with a machete, it was reported.
The incident happened on Boulevard Emile Jacqmain, with the main suspect being a Somali man, according to State broadcaster RTBF.