A group of residents from the Indian Ocean French island of Mayotte has been rounding up suspected illegal migrants and taking them to local police.
The move targeted around 100 "foreigners, Comorans and Africans", a member of the group told AFP.
Protests against the economic crisis and illegal immigrants from the Comoros islands have paralysed the island.
Mayotte has been in turmoil since mid-February, with roadblocks, a general strike and protests.
Locals complain that the arrivals of migrants are putting Mayotte's health, housing and education services under pressure.
About 70% of the 10,000 babies born every year in the island's only maternity hospital in the main town of Mamoudzou are born to illegal migrants, mainly from the Comoran islands, according to official statistics.
It is said to be one of France's busiest - to the point that the government is considering declaring the hospital as non-French territory so that children born there do not automatically qualify for French citizenship.
Mayotte is an island of 250,000 people that is part of the Comoros archipelago off the coast of Africa.
In 2011, it became the 101st French department, in accordance with the 2009 referendum.
It is a predominantly Muslim country, and although French is the official language, only about half of the population can read or write it.