Police said the migrants hail from countries including Congo, Mali, Guinea, Cameroon, Nigeria, Bangladesh and Pakistan. They include at least one pregnant woman and seven youths.
They were spotted early Thursday in a suburb of the country's divided capital after walking across a U.N. buffer zone separating the north from the internationally recognized south.
All 21 were taken to a migrants' reception center on Nicosia's outskirts.
Cyprus officials say most migrant arrivals to Cyprus come through the country's northern part where Turkish Cypriots have declared independence that's recognized only by Turkey.
This story has been corrected to show that the migrants were spotted Thursday, not Wednesday.
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