A group of six Greenpeace activists are scaling Britain's tallest building in protest at drilling in the Arctic.

The women, who evaded security guards at the 72-storey Shard in central London early this morning, said their action was intended to put Shell and other oil companies in the spotlight.

Greenpeace said the protesters were "artists and activists", adding: "If the six women reach the top - 310m above the pavement (1,017ft) - they will attempt to hang a huge work of art that captures the beauty of the Arctic.

"They chose to climb the Shard because it towers over Shell's three London offices, including the oil giant's global headquarters on the Southbank of the Thames.

"Shell is leading the oil companies' drive into the Arctic, investing billions in its Alaskan and Russian drilling programmes.

"A worldwide movement of millions has sprung up to stop them, but Shell is refusing to abandon its plans."

Watch the climb live below.

Metropolitan Police are at the site, a spokesman said.

A Shard spokesman said they were working to ensure the safety of the climbers as well as workers and visitors to the centre.

The demonstrators are live-streaming the climb from helmet cameras, with birds-eye views of their ascent being broadcast live at www.iceclimb.savethearctic.org.

They said if they do hang the Arctic artwork it will be the highest successful installation an art project since Philippe Petit tightrope-walked between the twin towers of the World Trade Center in 1974.

One climber, Victoria Henry, 32, a Canadian living in Hackney, London, said this morning: "We'll try to hang a huge art installation 310m up that will make Shell think twice before sending their rigs into the Arctic.

"It's going to be really hard work, it's going to be nerve-shredding for all of us and we may not succeed, but we're going to do everything we can to pull it off.

"Millions of people have called on Shell to get out of the Arctic but they're still trying to drill there anyway.

"If we reach the top we'll be able to see all three of Shell's London offices below us, meaning they'll be able to see us. Maybe then they'll stop ignoring the movement ranged against them."

The lead climbers are "free-climbing" (scaling the building without assistance) but are fixing safety ropes as they progress, they said.

They are carrying the huge work of art in backpacks and hope to install it this afternoon if they reach the summit.

A Metropolitan Police spokesman said: "We were called at 4.20am today to a group of protesters attempting to climb up the Shard.

"We are in attendance and monitoring the situation along with British Transport Police."

The group are believed to have got on to the structure by climbing on to the roof of the adjacent London Bridge Station.

A statement on the Greenpeace UK Twitter account said: "Look up London. We're attempting to scale the Shard, Europe's tallest skyscraper."

Greenpeace also posted a picture of the women posing together.

They are from the UK, Canada, Sweden, Poland, Holland and Belgium.

Greenpeace named them as Sabine Huyghe (Belgium), Sandra Lamborn (Sweden), Victoria Henry (Canada), Ali Garrigan (UK), Wiola Smul (Poland) and Liesbeth Debbens (Netherlands).

Swedish climber Sandra Lamborn, 29, said: "It's crazy. I've come to London to make a stand. We're drawing a line in the ice and saying to the oil companies, you come no further."

Greenpeace wants the area around the North Pole to be made a global sanctuary, off limits to industrialisation.

More than three million people have backed their call at savethearctic.org.

A Shard spokesman said: "The Shard is being used by protesters as part of a campaign.

"Our primary focus is on the safety of the protesters and the workers and visitors to the building.

"We are working with the relevant authorities to try to ensure the safety of those concerned."

The Shard was designed by architect Renzo Piano to resemble a shard of ice - which made it the "perfect" site for an Arctic art installation, Greenpeace said.

It is the tallest building in western Europe.

Upon external completion last year its crystalline facade transformed the London skyline.

It boasts high-quality offices, world-renowned restaurants, the five-star Shangri-La hotel, exclusive residential apartments and the capital's highest viewing gallery, The View from The Shard, offering 360 degree views.

A Shell spokesman said: "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 Shell personnel and customers, in mind."

The company said oil and gas production from the Arctic was not new.

"The Arctic region currently produces about 10% of the world's oil and 25% of its gas," it said in a statement.

"If responsibly developed, Arctic energy resources can help offset supply constraints and maintain energy security for consumers throughout the world.

"Shell has been operating in the Arctic and sub-Arctic since the early 20th century, giving us the technical experience and know-how to explore for and produce oil and gas responsibly.

"We work extensively with global Arctic stakeholders to research and develop standards and best practice on biodiversity, ecology, marine sound, oil spill prevention and response, safety and health."