Members of Extinction Rebellion Scotland, alongside peace activists from Trident Ploughshares, are staging the blockade at the north gate of the base on the Gare Loch in Argyll and Bute.
The all-female group placed three planters, which contained plants and flowers and were painted with the words “Safe”, “Green”, and “Future”, on the road on Friday morning.
An Extinction Rebellion protester is locked on to each planter so they cannot be moved, preventing access to the base, though emergency vehicles can still access the site via the south gate.
The activists said they are demanding a future safe from the “threat of nuclear weapons and environmental destruction”.
More than 15 campaigners are taking part but they are outnumbered by police officers who have erected screens as they attempt to remove the protesters.
As the police action began, demonstrators started singing.
Sarah Krischer, 28, an archaeologist and Extinction Rebellion Scotland activist, said: “Nuclear weapons are an existential threat to the entire world.
“Stockpiling weapons with the ability to wipe out all life in order to appear tough does nothing to keep either the UK or any other country safe.
“The ongoing environmental degradation caused by uranium mining and nuclear testing continues to be felt, particularly among Pacific island nations that are also the most threatened by climate change.
“We must come together to build a safe, more just future for all.”
A protester who gave her name only as Catherine said she wanted the UK Government to “dismantle Trident”, adding “we want a future that is sustainable and safe and nukes just aren’t that.”
“I feel a lot of anger and fear but also a lot of love. I’m doing this because I don’t want to die, I want to protect the people I love, the people around me, and I want a safe, green future for them.”
HM Naval Base Clyde, known as Faslane, is home to the UK’s nuclear deterrent.