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An environment protest group plans to blockade Dover Eastern Docks.
Extinction Rebellion (XR) will cut off two of the port's primary exit roads for up to four hours from 11am on Saturday, September 21.
The group warns that this will cause major traffic disruption in and around the harbour.
But it stresses that it has liaised with the police.
The theme is No Food on a Dying Planet, to stress fears of of food shortages and even starvation as the environment worsens.
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 will also include a family-friendly celebration of music, and information on how to help stave off the threat of starvation.
Similar protests in France and Belgium will coincide with this blockade.
XR had originally planned the civil disobedience on March 30, the day after the original Brexit date.
But the date for Britain leaving the EU was then postponed and XR decided to also put off its action so that it did not coincide with Brexit protests.
The group's other action has included occupying central London streets and bridges in April.
A Port of Dover spokesman said of the planned blockade: "We are aware of the protest plans and as a result, Port of Dover Police are working closely with Kent Police to ensure as minimal disruption as possible."