Police in Ho Chi Minh City said they have detained 21 foreign men for staying in the city without personal papers, some for as long as nine years.
The officers checked their rented apartments on Phan Huy Ich Street, Go Vap District, where 52 men were staying, on Monday night and many tried to flee.
Some fought back and the police had to use tasers to control them. Police said 21 of them failed to present valid passports and visas.
It is not immediately clear how and whether police officers could verify their nationalities. According to several media reports, the men came from African countries, including Nigeria and Cameroon.
Initial investigation found some of them have been staying in Vietnam without personal papers for eight to nine years.
Locals said the foreigners came to their neighborhood, renting ground-floor apartments to open shops and restaurants. Some suspected that several of the foreign men have also provided illegal sex services.
Police are investigating further.