Sex workers in China are subject to abuse by police, including physical assault, arbitrary detentions and extortion, a new report says.
The report by advocacy group Human Rights Watch (HRW) also describes cases of sex workers being coerced into HIV testing and sent to re-education camps.
Prostitution is illegal in China, and the government has sought to crack down on the trade.
However, the report says such efforts have made sex workers more vulnerable.
The report, which is based on around 140 interviews with sex workers, clients, police and specialists, said many sex workers were beaten by police in an attempt to coerce confessions.
"They attached us to trees, threw freezing cold water on us, and then proceeded to beat us," one sex worker told HRW.
Another said that police "deceived" her into signing a confession.
"The police told me it was fine, all I needed to do was sign my name and they would release me after four or five days," she said.
"Instead, I was locked up in [a] Custody and Education centre for six months".
Police often failed to investigate crimes against sex workers, the report said. Many sex workers were also afraid to report crimes to the police.
"I've been raped several times. But because I am a sex worker and selling sex is a violating of the law, I could be arrested. So I have never been willing to report to the police," one said.
There were also reports of police extorting money from sex workers and collaborating with clients during crackdowns.
"They arrange to have a client come into our venue and ask for sexual services. Once the services have started, the client calls the police, who arrest us both. They then fine the sex worker and split the money with the client," a sex worker said.
The report said that some women had been detained only for carrying condoms, which the police used as evidence of prostitution.
"This practice deters sex workers from carrying condoms, putting them at increased risk of HIV," the report said.
The report also said that sex workers were coerced into taking HIV tests, with the results being disclosed to third parties. Others said they were not given the results of their own tests.
"In China, the police often act as if by engaging in sex work, women have forfeited their rights," Sophie Richardson, HRW's China director, said.
The report calls on the Chinese government to "enact legislation to remove criminal and administrative sanctions against voluntary, consensual sex work".
It also says the government should end "the periodic 'anti-prostitution' mobilisation campaigns that have generated severe abuses against women engaging in sex work".
HRW cites UN estimates that put the number of female sex workers in China at between 4 and 6 million.