Climate activists inside five large containers have blocked the entrances to BP’s head office in central London.
The Greenpeace protesters used cranes to transport the heavy boxes into place at St James’s Square in the early hours of the morning.
Other campaigners abseiled down the side of the building to block windows and display banners.
Officers from the Met Police are at the scene. No arrests have been made.
Greenpeace said they were carrying out the action to call on BP to end exploration for oil and gas, and only invest in renewable energy.
One campaigner, called Morton, told the BBC the group was planning a “long-term occupation of BP’s headquarters”.
A BP employee said they had not been told what was happening.
“I’m thinking to go home because it will take the police a while to get the protesters abseiling off the building,” the staff member said.
BP has been approached for comment.