The police raided four massage parlours in Rangoon, Balestier and Race Course roads yesterday.
Six foreign women, aged between 29 and 50, were arrested for offering sexual services.
Two traditional Chinese medicine (TCM) centres in Rangoon Road were the first to be raided within an hour of each other around 3pm by the Central Police Division.
Instead of TCM practitioners, two female masseuses were found in each centre. Condoms were also found in the massage rooms. Three of the women were arrested after they were found to be offering sex.
The licensed TCM practitioners were not present at both locations, which police said is an offence.
The police then raided two more unlicensed massage establishments disguised as beauty spas in Balestier and Race Course roadsaround 5pm. Three more women were arrested for offering sex.
The beauty spas provided massage services, which is an offence, said the police.
The operations are part of ongoing efforts to conduct regular enforcement checks on massage establishments.
Last November, the police nabbed 81 women in raids at unlicensed massage parlours and public entertainment outlets in Thomson, Paya Lebar, Selegie, Outram and Bukit Timah.
In June last year, 75 people were arrested in a four-day enforcement raid on such centres.