Police and anti-immigration protesters have clashed outside the entrance to Dover harbour.
Several officers were seen restraining one person on the ground and police confirmed they had made an arrest.
It comes as rival protests over migrants reaching the UK in small boats take place in the town.
The Kent Anti-Racism Network said it wanted to show “solidarity” with refugees, while opposing groups want “to protect Britain’s border”.
A message was beamed on to the White Cliffs overnight by humanitarian charity Freedom From Torture.
It read: “Rise above fear. Refugees welcome.”
Police have concentrated their officers in Market Square and at the railway station, and officers on horseback are also monitoring the situation.
A group of about 60 people shouting “freedom” has been moving along Dover seafront, with many wearing Union flag masks and carrying flags.
But, addressing a crowd of about 100, Peter Keenan from Kent Refugee Help said when society sees people who are fleeing war and turns them away “that says something about the state of your society”.
He continued: “We are not those people.”
In a tweet, the Port of Dover warned there was disruption on the A20 because of the protest and advised the local community to consider alternative routes and travellers to allow plenty of time for their journeys.
Protesters blocked the dual carriageway in both directions, leaving traffic at a standstill, with some singing Rule, Britannia! as they marched towards the town.
Many wore Union flag face masks and carried banners.
There were further clashes with a group of at least 50 police officers by the A20.
Officers have been moving protesters along the road towards the town centre.
Ch Supt Nigel Brooks said: “As a force, it is our responsibility to facilitate peaceful protests, however we will not tolerate violence or disorder.
“Anyone planning to visit Dover with the intention of committing offences should be aware they are not welcome here and that we will seek to prosecute anyone who breaks the law.”
It is thought that groups from across the country have travelled to Dover.
Dover MP Natalie Elphicke had urged people to “stay away” to prevent a second wave of coronavirus.
A Home Office spokeswoman said: “We are aware of potential protests in Dover and have contingency plans in place to minimise any potential disruption to operational activity.”
Figures compiled by the BBC show at least 5,196 people have crossed the English Channel in about 318 boats in 2020.