Police rescued six women from a suspected brothel in Birmingham yesterday as part of a nationwide swoop on sex trafficking.
A man was also arrested in the dawn raid at what was believed to be on a house in the Speedwell Road area of Balsall Heath.
However, a local street-watch campaigner expressed his surprise that there was suspected vice activity in the semi-detached house, which was guarded by police yesterday.
Raja Amin, chairman of Balsall Heath streetwatch, said: "There used to be activity about three years ago on that road, but we have heard of nothing since.
"It is very surprising. Especially as there was supposedly six girls at this address."
The raid was carried out under Operation Pentameter, which aims to help women trafficked into the country and forced into prostitution.
Residents living near the run-down house said they regularly saw between four and six Chinese men coming and going, and had assumed they were students.
One neighbour, who did not wish to be named, said: "Sometimes these guys would have girls with them when they came to the house but we just assumed they were all foreign students - the university's just round the corner."
Police carried out simultaneous swoops on addresses in London and Berkhampstead in Hertfordshire following a five-month intelligence operation by the Metropolitan Police and West Midlands Police.
A total of 19 women were rescued in the biggest operation so far under Operation Pentameter, launched in February.
Thirteen were found at a suspected brothel in Paddington, west London, and were taken to specialist reception centres where they were seen by health officials and interpreters.
Police arrested 11 people, including the suspected ring-leaders, believed to be Vietnamese.
Last September, Cuddles massage parlour, in Hagley Road, Bearwood, was raided and a number of women from eastern Europe were found.
A Hungarian couple have since appeared in court accused of human trafficking for the purposes of prostitution.
Chief Supt Ian Dyson said of yesterday's Operation Pentameter raids: "I hope this will send out a clear message to the organisers of this vile trade that we will track them down and we will seize their assets.
"I would also like to say to the men that use prostitutes, 'you are fuelling this trade'."
Mr Dyson said yesterday's operation was aimed at arresting men behind the trafficking of women into the UK for prostitution.
The network is suspected of trafficking Malaysian women into the country for the purposes of prostitution. Police believe that the organisers were making tens of thousands of pounds from the racket.
Before yesterday's raids, 44 women and two girls had been rescued since the start of Pentameter in February.