Campaigners have chained themselves to the gate of a naval base in protest against the nuclear missiles stored there.
The Scrap Trident coalition wants Scotland to be allowed to "lead the way to a world free of nuclear weapons" and more than 100 of its supporters are demonstrating at Faslane Naval Base, in Argyll, the home of the UK's Trident weapons system.
Around 20 protesters chained themselves to the north gate of the base while sitting or lying on the ground, and eight people are "locked on" to the south gate.
Police issued a warning to the group at the north gate then officers started using cutting equipment to separate them.
The blockade follows a weekend of action calling on the UK Government to scrap Trident and use its budget to fund welfare, education and health instead.
Ray Davies, 83, a Labour councillor for Caerphilly in Wales, travelled to Scotland for the protest. He sat on the road in front of the north gate holding a Welsh flag.
"I am here on behalf of the people of Wales. I am here on behalf of my seven grandchildren, my 12 great-grandchildren and for the children of the world because we want a world that's not poisoned. We want a planet that can live in peace and can have a future," he said.
"There can never be a peaceful world with nuclear weapons, not just nuclear weapons but the pollution from the power stations that they need. Everything that is connected to nuclear weapons is slowly but surely poisoning this beautiful planet.
"I will never, ever give up. As long as there is a fire burning in my belly."
A convoy of buses carrying protesters arrived at Faslane at 6.45am. The group of around 100 people started their protest by singing as some chained themselves to the gate.
Organisers said disability rights campaigners, students, pensioners, trade unionists and environmentalists are taking part in the protest.
Nicole MacLean, a student from Falkirk, chained herself to the north gate.
"We want to set a precedent for other countries," she said.
"I know it's hard with nuclear to give it up but if we've got people behind supporting it, saying this is what we want, I think it sends a positive message to the world to get rid of nuclear weapons.
"It's really important that if something bad is happening, you are bearing witness to it and let the Government know we are still watching them and know what they are doing."
Jonathan Shafi, from the Radical Independence Campaign and member of the Scrap Trident coalition, said: "Instead of spending billions on Trident, weapons and warfare, money should be spent on schools, hospitals and services.
"We want to play a role right across the world, in terms of disarmament, to say that nuclear weapons are an obscenity and should be confined to the past and we should be looking forward to a more positive future."
On Saturday hundreds of supporters of the anti-Trident cause marched through the centre of Glasgow and came together for a rally in George Square.
The Faslane blockade is said to be one of more than 100 similar protests in dozens of countries in what is a global day of action against military spending.