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About 100 environmental campaigners have gathered for a planned blockade at Dover Eastern Docks today.
Protest group Extinction Rebellion (XR) is cutting off two of the port's primary exit roads for four hours.
It is reported that some protesters have glued themselves to an westbound section of the A20 in the town, with witnesses claiming one was taken away in a stretcher after sticking their hands to the road.
Police have confined the protesters to a cordoned off area, warning they risk arrest if they leave.
A notice from Kent Police says the measure has been taken "due to the time and place of this intended public assembly, its purpose and the intention of the organisers."
A police spokesman said: "Following consultation with partner agencies, including the Port of Dover and Highways England, a designated area has been created in Townwall Street to allow a peaceful protest.
"The event organisers have been notified of this and, in order to ensure the protest remains peaceful, a small number of attendees have been advised that choosing to leave the designated area to cause disruption, or inciting others to cause disruption, could lead to proportionate enforcement action."
Unconfirmed reports say 10 arrests have been made, including a 91-year-old man.
The Port of Dover has tweeted to say traffic is moving freely in and out of the docks, although ferry operator DFDS has reported delays in boarding and discharging passengers.
The protest group previously warned that this will cause major traffic disruption in and around the harbour.
Extinction Rebellion also took over Dover Castle and hung a banner on the castle wall in support of the blockade.
Chris Atkins, of XR Dover, said: “The government is saying and doing precious little to prepare us for what we know is coming.
“As climate change develops, millions of ordinary Britons will face the real and growing threat of food shortages, hunger and starvation.
“Extreme storms and floods are already causing major crop failures across the world, with high temperatures also hitting livestock agriculture.
“This growing crisis may seem far away now but, as the UK imports around half the food it consumes, we are extremely vulnerable to these climate impacts.
“The government must tell the truth and act now.
"The longer we kick the can down the road, the greater the risks of price hikes, food shortages, hunger and, ultimately, starvation here in Britain.
“We’re sorry for disrupting journeys but the British public deserves to know the truth.
"If the government refuses to even talk about this, then someone else must.”
The day also includes a family-friendly celebration of music and information on how to help stave off the threat of starvation.
Speaking to KentOnline at the protest, XR member Peter Batt said: "Climate change isn't just about warming temperatures, it is also disrupting food production.
"As a nation, we import about half of the food that we consume, so we are very vulnerable to changes in global patterns in that respect.
"We are actually directing this (protest) at the government, because we want them to start talking about this rather than ignoring it and actually start a process of taking action so we can improve our own agricultural resillience.
"We are not actually directing this at ordinary people although it may feel that way because obviously we are causing disruption, but we feel that we don't really have any choice.
"If the government are not going to listen to their own experts and scientists then we believe we have to raise public awareness so the public will start putting pressure on the government.
"Even in our short 10 month history, this is a tried and tested approach and we have, the research would suggest, significantly changed the nature of the narrative on all climate change issues."
Similar protests in France and Belgium are coinciding with the blockade.