The Immigration Department said on Monday six foreign domestic workers have been arrested for allegedly providing unlicensed dental services from a tenement unit in Sham Shui Po.

Dhubal Tai, chief immigration officer of the Foreign Domestic Helpers Special Investigation Section, said the six, women aged 34 to 60, were apprehended in a raid, with preliminary findings indicating that two of them acted as dentists while the other four served as assistants.

Thirteen Filipino nationals found at the scene are believed to have been customers seeking treatment.

Officers seized evidence that included instruments for teeth cleaning, braces and denture making.

"The hygiene conditions at the scene were deplorable," Tai said.

"The so-called surgery room merely contained a sofa, distilled water, tissues, towels, air fresheners, a wash basin and rudimentary surgical instruments.

"When we arrested the so-called dentists, they were wearing ordinary clothes. There was no evidence that their clothing, medical supplies or tools had undergone any sterilisation.

"Medical waste was also discarded haphazardly, posing a significant risk of cross-infection."

Tai said clients were reportedly referred through word of mouth within the foreign domestic worker community and that fees ranged from HK$150 to HK$500 per session.

"Preliminary investigations show that the six foreign domestic workers provided dental services, including teeth cleaning, orthodontic treatment and denture making, to fellow foreign domestic workers every Sunday at a tenement unit, which is located in a secluded area," he said.

"None of these six workers have received any formal dental training in Hong Kong or elsewhere, nor do they hold any professional dental qualifications. Our investigations reveal that they learned dental work through online videos."

Tai said the suspects are accused of violating their conditions of stay, which state that foreign domestic workers must not be employed by any other person for any other duties, as well as for practicing dentistry without registration.

He said their employers were reportedly unaware of their illegal activities and that the investigation remains active, with further arrests possible.

He said the arrest operation is part of a series of Immigration Department crackdowns on illegal workers.