Twelve people have been arrested after being cut free from a gate at Faslane naval base, according to anti-nuclear protesters.
The Scrap Trident Coalition says it has blocked all entrances to the base, which is home to the UK's Trident nuclear weapons system, and estimates it will take several hours to clear the entrance to the south gate.
A group of protesters have covered themselves in red paint to form a red line to symbolise their "total rejection of the UK's weapons of mass slaughter".
Scrap Trident spokesman Brian Larkin said: "The scene here is a joyful one, with singing and dancing and the brilliant samba beat from Rhythms of Resistance. The blockade has been a tremendous success."
Protesters gathered outside every gate to the base from 7am in an attempt to stop workers from entering, with the blockade due to last until 3pm.
Organisers estimate there are up to 150 demonstrators outside the north gate, with 250 across all the gates.
A Scrap Trident spokesman said: "We are delighted that, in spite of a big police presence, people have been able to peacefully and imaginatively shut down the WMD base, putting their bodies on the line in their utter rejection of what Trident represents."
Patrick Harvie, co-convenor of the Scottish Greens and MSP for Glasgow, is among those taking part.
He said: "Trident is an obscenity. Through direct action and through the ballot box we can make the case for the UK to play a new role on the world stage.
"By pursuing peace, a global deal on climate change and ending the arms trade we can stand tall rather than clinging to outdated and dangerous status symbols.
"By choosing to disarm Trident we can re-skill workers on the Clyde to provide defence of the strategically important northern seas, and diversify our economy for social good."
The blockade is part of a series of events organised by Scrap Trident to focus attention on the UK's nuclear deterrent in the run-up to May's General Election.
Thousands attended a march and rally in Glasgow city centre earlier this month to call on the UK Government to abandon plans to replace Trident.
The nuclear weapons system came to the fore of the campaign last week after Defence Secretary Michael Fallon confirmed that a Conservative government would go ahead with the construction of four new Trident nuclear missile submarines to replace the existing fleet of ageing Vanguard-class boats.
He warned that the deterrent would be put at risk by the prospect of Labour leader Ed Miliband entering into a pact with the anti-Trident SNP in the event of a hung parliament in May.
But Mr Miliband insisted Labour is fully committed to renewing the Trident submarine missile fleet.
Over the weekend, leading figures in music, the arts and science, including Nobel prize winner Professor Peter Higgs, comedian Frankie Boyle and Mercury Prize-winning band Young Fathers, called for the nuclear deterrent to be scrapped in a letter to the Observer.
A Faslane spokesman said: "The MoD recognises the democratic right of individuals to participate in lawful and peaceful protest activities.
"The MoD police and Police Scotland are seeking to facilitate safe and peaceful protest activity but any breaches of criminal law will be dealt with in an appropriate manner."
He said the operational output of the base is not being affected by the protest activity as they have contingency plans in place.
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