Extinction Rebellion protesters have blocked access to the BBC's headquarters – with staff reportedly unable to enter or leave through the main entrance.
Dozens of demonstrators camped outside New Broadcasting House in central London on Friday morning.
They carried banners urging the corporation to end its "silence" on climate change, while others taped over their mouths to suggest their voice had been taken away.
BBC workers reported being unable to get in or out of the building, among them financial journalist Paul Lewis, who tweeted: "No one in no one out. Locked down."
The demonstration is the latest in a week of planned protests which has already seen at least 1,112 people arrested since Monday, Scotland Yard said.
On Thursday, demonstrations focused on London City Airport, where protesters attempted a "Hong Kong-style occupation" of the terminal building, with hundreds blocking the main entrance.
One demonstrator, former Paralympic cyclist James Brown, climbed on top of a British Airways jet, prompting criticism from Metropolitan Police Commissioner Dame Cressida Dick, who described the act as "reckless, stupid and dangerous".
