Two environmental protesters are spending a night on a port gantry after a protest targeting VW diesel cars being delivered to the UK from Germany.
The Greenpeace protest saw two others board a ship at Sheerness port in Kent to prevent the unloading of vehicles.
Forty people also entered the port's import park and removed thousands of keys from cars to immobilise them.
The keys were handed to the two who climbed the lighting gantry. Volkswagen said it was aware of the protest.
A Greenpeace spokesman said the two on the ship had been detained along with a third activist.
Kent Police said a man had been arrested on suspicion of aggravated trespass, and the other two, a man and a woman, had been arrested under the Merchant Shipping Act on suspicion of entering a vessel.
'Ship forced to leave'
Greenpeace said the ship had been delivering vehicles to the vehicle park at Sheerness, where several thousand VW diesel cars were awaiting distribution to suppliers.
The group had said the protesters on the ship planned to stay on the vessel until Volkswagen agreed to return the cars to Germany.
Campaigners also said they had forced the 23,000-tonne ship cargo ship, the Elbe Highway, to turn round.
The vessel left Sheerness earlier and was anchored off Margate, but Volkswagen told the BBC the plan was for the ship to return to Sheerness by Friday morning.
A spokeswoman for Peel Ports, which owns the Port of Sheerness, confirmed that Greenpeace protesters had illegally entered secure areas and port staff had been working with the police, Greenpeace and Volkswagen to resolve the situation.
Kent Police said officers received reports of a protest at the Port of Sheerness at 08:52 BST.
A police spokesman said officers worked with port staff to bring the situation to a safe conclusion while facilitating a peaceful protest.
He said: "Officers continue to work with Peel Ports and the Maritime and Coastguard Agency to ensure the safety of remaining protesters and the public."
In a statement, a Volkswagen spokesman said: "We are aware of a protest this morning at the Sheerness port in Kent.
"The ship contains a variety of Volkswagen Group vehicles, including petrol, diesel and plug-in hybrid models. The diesel vehicles, which are the subject of the protest, meet strict Euro-6 standards."
In September 2015 VW admitted to US regulators it had cheated on emissions tests there using software installed in as many as 11 million diesel vehicles sold worldwide - the majority of them in Europe.
In March the company pleaded guilty to conspiracy to commit fraud, obstruction of justice and entry of goods by false statement as part of a $4.3bn (£3.5bn) agreement with the US regulators over the scandal.