Channel 4 News reporter Jim Blakey says police at The Shard think it would be "too dangerous" to attempt to seize the demonstrators currently trying the climb the building.
The met police says it has rope teams ready at the shard but suspect it will be too dangerous to go up and seize the greenpeace protesters..
Nottinghamshire woman Ali Garrigan, 27, is one of the activists climbing The Shard today, according to Greenpeace:
Cold and windy 100m up but smiles and snacks all round
In a statement on the Greenpeace website, she said: "We're climbing this building because it's time to draw a line in the ice and say to the oil companies you come no further."
The incredible #iceclimb team are 85m up the Shard and it's 310m tall - go go go!
Responding to the demonstration at The Shard in protest at Arctic drilling by oil firm Shell, a company 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.
Greenpeace has released video which shows how six activists accessed exterior of The Shard before attempting to reach the top of the 310m-high building.
One of the campaigners said they plan to unveil a "huge artwork" near the summit of the structure.
Greenpeace says Victoria Henry, a Canadian living in London, is one of the climbers scaling The Shard.
This morning she tweeted about the "months of training and secrecy" leading up to the stunt:
Months of training and secrecy end here. I'm scared but incredibly excited about today #iceclimb
Greenpeace said the Shard 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."
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 Shard is is 1016ft (309.6m) high
- The area of the glass facade is 602,779 ft squared (56,000m squared), which equals eight football pitches
- There are 306 flights of stairs
- There are 44 lifts, including double-decker lifts
- There are 72 occupiable floors
A spokesman for The Shard said: "The Shard is being used by protestors as part of a campaign.
"Our primary focus is on the safety of the protestors and the workers and visitors to the building.
"We are working with the relevant authorities to try to ensure the safety of those concerned."