Smoke bombs were let off and bricks thrown as police turned out in force to oversee hundreds of far-right demonstrators marching through town.
They clashed with anti-fascist demonstrators, leaving five people with minor injuries.
Kent Police said it seized more than 20 weapons including a knuckle duster.
Police said their operation ended at 17:00 GMT after they had arrested individuals for possession of offensive weapons, breaching the peace and public order offences.
Banners and placards carried by the right-wing marchers included those from the North West National Front, neo-Nazi organisation Combat 18 and the Scottish Defence League.
Counter-demonstrators included members of Kent Anti-Racism Network, anti-fascist group Antifa and people with Socialist Worker placards. They were addressed by Diane Abbott, shadow secretary of state for international development.
Earlier, six people were arrested on suspicion of violent disorder at a service station on the M20 which was closed after several coaches believed to be on the way to the demonstrations were damaged.
Police said officers were called to a disturbance at Maidstone services at junction eight at 10:51 GMT. Two coaches had swastikas daubed on them in blood following a clash between two rival groups.
A coach which left the scene was stopped at junction 11 services at Westenhanger.
During the day police took away weapons including a knife, pieces of wood, glass, hammers and bricks.
A police spokesman said he could not comment on the motives of those involved, or what groups they may or may not have been a part of.
Police warned on Friday the demonstrations were expected to attract large numbers of protesters, with businesses and residents told to expect disruption.

Two of the songs come from the Don Quixote musical Man of La Mancha, which was a Broadway smash in the 1960s.
"As far as I am concerned, Don Quixote is the most metal fictional character that I know," the Hobbit star said.
"Single handed, he is trying to change the world, regardless of any personal consequences. It is a wonderful character to sing."
The album also includes an ear-splitting version of Frank Sinatra's My Way - originally written by Paul Anka - which Lee originally released in 2006.
"My Way is a very remarkable song," said the star in a YouTube preview.
"It is also difficult to sing because you've got to convince people that what you're singing about is the truth."
Sir Christopher launched his singing career in the 1990s, with an album of Broadway tunes, including I Stole The Prince from Gilbert and Sullivan's The Gondoliers, and Epiphany from Sweeney Todd.
In 2010, his album Charlemagne: By the Sword and the Cross, which told the story of the first Holy Roman Emperor won a Spirit of Metal Award from Metal Hammer magazine.
His latest release, Metal Knight, is a collaboration with Italian symphonic metal band, Rhapsody Of Fire.
"I associate heavy metal with fantasy because of the tremendous power that the music delivers," he has said.
The actor is known for his numerous appearances as Dracula, as well as playing Scaramanga in The Man With The Golden Gun, Saruman in Lord Of The Rings, and Count Dooku in the Star Wars prequels.
Last year, he was presented with a fellowship from the British Film Institute.

The body of Malcolm Ballantyne, known as Malky, was found at his home in Glebe Place by a family member shortly after 13:00 on Friday.
A post-mortem examination is taking place but police are treating the death as suspicious.
Officers are trying to trace Mr Ballantyne's movements on Thursday and Friday and are also checking CCTV.
Det Ch Insp Gary Cunningham said: "Malky was found yesterday by a family member who is obviously distraught at what has happened.
"He is a well-known character in the area and has a routine where he visits and socialises in various pubs in Stevenson most days - generally in the morning.
"We are keen to find out if anyone saw Malky between 1000 hours on Thursday 20 August and 1300 hours on Friday 21 August."
Door-to-door inquiries are taking place in Saltcoats and Stevenson and there are extra uniformed patrols in the area.
Three people were arrested amid violent scenes as groups demonstrating against immigration clashed with anti-racism protesters in Dover.
[NEXT_CONCEPT]
Actor Sir Christopher Lee is marking his 92nd birthday by releasing an album of heavy metal cover versions.
[NEXT_CONCEPT]
Investigations are under way after the death of 72-year-old man at a flat in Saltcoats, in North Ayrshire.