Emergency services have cordoned off the area surrounding Big Ben after a man scaled one of the buildings in the Palace of Westminster.
Video on social media shows a barefoot man standing on a ledge holding a Palestinian flag several metres up Elizabeth Tower, which houses the Westminster clock and its world-famous bell.
At least nine emergency service vehicles lined Bridge Street in central London and crowds looked on from beyond a police cordon.
A Met police spokesperson said: “At 7.24am on Saturday 8 March officers were alerted to a man climbing up the Elizabeth Tower at the Houses of Parliament.
“Officers are at the scene working to bring the incident to a safe conclusion. They are being assisted by the London Fire Brigade and the London Ambulance Service.”
Bridge Street, which is at the north end of Westminster Bridge, was closed to allow the emergency services to deal with the incident, police said. It is understood one exit of Westminster station is also closed, but there is no disruption to tube services and passengers can use other exits.
A spokesman for the London fire brigade said: “Firefighters are responding alongside the Metropolitan Police service to reports of a person scaling the Palace of Westminster.”
The LBC reporter Shivani Sharma reported that the protester had been on the Elizabeth Tower for almost three hours as of 10.20am. The man is reportedly saying “peaceful protesters are being brutally arrested” and “I’ve brought the protest to the so-called hub of democracy in the UK” to onlookers below.
Pro-Palestine activists also staged an action at one of Donald Trump’s golf courses in Scotland on Saturday. Palestine Action activists spray-painted the clubhouse at the Trump Turnberry resort and dug up some of the greens overnight.

In a video the group posted on social medi, the words “Gaza is not 4 sale” are sprayed on the grass.
The group said its action was a “direct response to the US administration’s stated intent to ethnically cleanse Gaza” after “having laid out plans to ‘clean out the whole thing’ and forcibly displace its population”.
A spokesperson said: “Palestine Action rejects Donald Trump’s treatment of Gaza as though it were his property to dispose of as he likes. To make that clear, we have shown him that his own property is not safe from acts of resistance. We will continue to take action against US-Israeli colonialism in the Palestinian homeland.”