Greenpeace protesters try to climb Shard

Six women were attempting to climb London's 72-storey Shard skyscraper on Thursday morning in protest over Arctic oil drilling, the environmental group Greenpeace and police said.

The six "artists and activists" evaded security guards at 4am to begin the unauthorised attempt to scale the tallest building in the European Union, which stands 301 metres (1,017 feet) tall, Greenpeace said.

"They chose to climb the Shard because it towers over Shell's three London offices," it said in a statement.

"Shell is leading the oil companies' drive into the Arctic, investing billions in its Alaskan and Russian drilling programmes. A worldwide movement of billions has sprung up to stop them, but Shell is refusing to abandon its plans."

In a tweet, the group introduced the climbers as "Sabine, Sandra, Victo, Ali, Wiola and Liesbeth" and posted a photo of them before the climb, wearing helmets and harnesses and sporting Greenpeace-branded gear.

They were "free climbing" without assistance but would attach safety ropes as they progressed, Greenpeace said, while a live video feed of the climb was being broadcast online.

A spokesman for London's Metropolitan Police said, "We were called at twenty past four this morning. We have six protesters attempting to scale the outside of the Shard.

"We have officers down there, monitoring the situation. The event is still ongoing."

Greenpeace said that if the protesters reached the top of the glass and steel structure, "which is far from likely", they would hang a "huge work of art which captures the beauty of the Arctic".

The Shard, designed by Italian architect Renzo Piano was financed by the Qatari government and was inaugurated in July 2012 on completion of its exterior, but work on the interior continues.

Critics have slammed its dominance of the London skyline and said it compromises views of landmarks such as St Paul's Cathedral and the Tower of London.

Oil giant Shell has been involved in oil extraction in Alaska since the 1950s, and said in 2012 it had completed top-hole drilling for two wells in the Arctic, the first drilling in the region in more than a decade.

But in February it put its controversial oil drilling plans for the Alaskan Arctic on hold through 2013, following problems with its two drilling rigs, the Noble Discoverer and the Kulluk.

The Kulluk washed ashore after breaking loose from towing vessels in stormy seas in southern Alaska in January and the Noble Discoverer has been cited by the US Coast Guard for safety and operational deficiencies.

Shell has sent both to Asia for maintenance and repairs.

Experts believe the Arctic holds 90 billion barrel of oil reserves and 30 percent of the world's untapped natural gas -- resources made more accessible as climate change causes Arctic ice to recede.

But the challenging natural environment makes extraction difficult and costs high, while activists warn of the risk of accidents and oil spills in the pristine Arctic environment.