Police were called to the Palace of Westminster after a man was seen climbing the tower that houses Big Ben.
Videos shared on social media show a barefoot man standing on a ledge several meters above the ground on the Elizabeth Tower, holding a Palestinian flag.
At least nine emergency service vehicles lined Bridge Street in central London as crowds gathered behind a police cordon to watch the situation unfold.
A spokesperson for the Metropolitan Police stated, "At 7:24 AM on Saturday, March 8, officers were alerted to a man climbing the Elizabeth Tower at the Houses of Parliament. Officers are currently at the scene, working to resolve the incident safely, with assistance from the London Fire Brigade and the London Ambulance Service."
By around 10 AM, three emergency personnel were lifted several meters using a fire brigade aerial ladder platform, with one officer communicating with the man via a megaphone.
To ensure the safety of emergency responders, police have closed Bridge Street at the northern end of Westminster Bridge.
A London Fire Brigade (LFB) spokesperson confirmed, "Firefighters are working alongside the Metropolitan Police Service in response to reports of a person scaling the Palace of Westminster." LFB added that crews from Lambeth, Chelsea, Soho, and Islington fire stations had been deployed to assist.