Seven people who had been granted asylum seeker status in Hong Kong were among a group of illegal workers rounded up during a police raid at a catering facility in a Kowloon industrial building early on Sunday.

The six Vietnamese and one Bangladeshi, who include a mother and her daughter, have been charged with contravening the conditions of their stay. Asylum seekers and refugees are not permitted to work while their claims are being processed by the government and United Nations.

Police said the raid was launched after reports of suspicious activities by people working in a dishwashing facility. The detained workers, who are aged between 19 and 46, tried to escape but were intercepted by constables who waited in ambush, according to Oriental Daily News.

Investigations are underway to see if triads were involved in the factory operations or controlled any of those detained. The manager, a Hong Kong resident, has been summoned by police to assist in the inquiries and may also face charges of employing illegal workers.

More than 3,400 illegal foreign workers were arrested or put on trial in the first 11 months of 2018, including 1,007 asylum seekers.

Restaurant operators and catering firms face a persistent labor crunch and some seek to fill vacancies by hiring illegally. Some even cooperate with human-smuggling syndicates to woo people from South Asia.

According to police, people recruited in this way typically go to work late at night or early in the morning to avoid government inspections.