A demonstrator dressed as a polar bear is taken away by police. Picture: Gordon Terris
Greenpeace activists are hoping to shut off petrol to at least 12 petrol stations in Edinburgh.
The group's protest will also see around 100 petrol stations in London targeted.
The protesters said they planned to use an emergency shut-off switch to stop petrol going to the pumps, then removing a fuse to delay it being switched on again.
The first station targeted was the Shell garage in Edinburgh's Dalry Road, where they attempted to scale the roof.
Police and fire crews said they were at the scene.
Shell is due to begin drilling at two offshore sites in the Alaskan Arctic in the coming weeks.
Greenpeace's Sara Ayech said: "The oil giant Shell is preparing, for the first time, to unleash a drilling fleet of huge vessels upon the fragile and beautiful Arctic, home of the polar bears.
"It's time to draw a line in the ice and tell Shell to stop. That's why today we're going to shut down all of Shell's petrol stations in the capital cities of London and Edinburgh. We've got dozens of people who will hit over 100 Shell garages throughout the day.
"An oil spill in the Arctic would be catastrophic for wildlife such as walruses and whales, and Shell knows full well that it would be impossible to clean up after such devastation. The Arctic must be saved, and made a global sanctuary where oil drilling is banned."
A spokesman for Shell said: "Shell recognises that certain organisations are opposed to our exploration programme Offshore Alaska, and we respect the right of individuals and organisations to engage in a free and frank exchange of views about our operations.
"Recognising the right of individuals to express their point of view, we only ask that they do so with their safety and the safety of others, including the general public and Shell personnel, in mind.
"Shell has met with numerous organisations and individuals who oppose drilling offshore Alaska. We respect their views and value the dialogue. We have extended this same offer for productive dialogue to Greenpeace."
Greenpeace broadcasted its action online, updating details about station closures and arrests.
At 9am, the charity announced it had "closed down" more than 40 stations, including Old Ford in east London, Fulham Cross in west London, and Hornsey in north London.
It said nine arrests had been made - four in London and five in Edinburgh.
Scotland Yard did not confirm the arrests, but said it was aware of disruption at Shell garages.
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