Migrant numbers are increasing in the port town a year after the notorious “Jungle” camp was bulldozed.
Up to 200 migrants armed with sticks and iron bars have clashed in five mass brawls near Calais, according to French authorities.
Twenty-one migrants and six riot police officers were injured in the fights, which broke out between Monday night and Tuesday afternoon.
Around 150 were involved in the last brawl, which began on the A16 road leading out of the centre of Calais and moved on to a highway, the Pas-de-Calais prefecture said.
Authorities said the majority of those involved were Afghans and Eritreans.
Four other fights began late on Monday and continued until dawn as police dispersed the groups with tear gas.
None of the injuries is thought to be serious.
Voix du Nord newspaper said the violence had held up traffic around the town.
Police detained seven migrants for questioning and placed 20 others in administrative detention – meaning they could be expelled from France.
Last year, around 7,000 migrants were cleared from the makeshift “Jungle” camp in Calais, but people hoping to get into Britain by crossing the Channel in trains or ferries are steadily returning.
Around 400 migrants are now estimated to be in the Calais area, authorities estimate, although aid agencies put the number at closer to 600.
Interior minister Gerard Collomb said earlier this month that although there are fewer migrants in Calais compared to last year, some 30,000 attempts to get into the Eurotunnel complex or on to ferries have been made since the start of 2017.
In July, the interior minister announced that two special centres to shelter migrants would be opened in Calais.
But the shelters are aimed at speeding up assessments – including possible deportation – and are not compulsory.