Four migrants were in a critical condition after being shot during a brawl between Eritrean and Afghan migrants in the northern French port city of Calais on Thursday, local authorities said.

Another two migrants suffered less serious gunshot wounds and 12 others had other injuries, the local prefecture said, adding the numbers could change.

French Interior Minister Gerard Collomb said he would travel to Calais on Thursday evening to review the situation following what he called "the serious incidents".

Several scuffles broke out mid-afternoon between migrants from different communities, the prefecture said.

"The police intervened to protect Afghan migrants who were threatened by 200 migrants of Eritrean nationality," it said.

Authorities said around 600 migrants are in the Calais region, though humanitarian groups put the number at 800.