As many as 200 migrants have clashed near the French city of Calais, using sticks and iron bars in five battles pitting mainly Afghans against Eritreans, authorities said.
The prefecture of the Pas-de-Calais region said up to 150 migrants were involved in the latest mass brawl on Tuesday afternoon.
It said five people were slightly injured before police dispersed the group.
The prefecture said four previous fights started late Monday and continued until dawn. Six riot police were injured, along with 16 others.
Police detained seven migrants and put 20 others in administrative detention, meaning they risk expulsion from France.
Authorities cleared some 7,000 migrants from a makeshift camp in Calais last autumn, but people hoping to enter Britain illegally via the English Channel are steadily returning.