A Hong Kong woman was convicted Tuesday of beating and starving her Indonesian maid, keeping her prisoner in a "torture" case that sparked international outrage and spotlighted the plight of migrant domestic workers.

The verdict, read out to a packed courtroom, was met with cheers by activists and supporters of Erwiana Sulistyaningsih, a former domestic helper who has become the face of a campaign for improved workers' rights in the financial hub.

Pictures of the injuries sustained by the 24-year-old, who was admitted to hospital in her home country emaciated and in a critical condition, at the hands of mother-of-two Law Wan-tung fuelled anger in Indonesia and shocked Hong Kong.

Sulistyaningsih hailed the ruling but called for reforms to ensure Hong Kong employers no longer treated domestic workers "like slaves".

She said that while she forgave her abuser, she hoped Law would receive the maximum seven year jail term when sentencing is announced on February 27.

"She was, for want of a better word, a prisoner in those premises," Judge Amanda Woodcock said, referring to Sulistyaningsih.

"She was completely isolated, and (this) helps explain why this abuse could go on for so long without her retaliating or anyone knowing."

"When Erwiana left Hong Kong she was a shadow of her former self."

Law, 44, was found guilty of 18 of the 20 charges laid against her, including grievous bodily harm, assault, criminal intimidation and failure to pay wages.

She lowered her head but appeared to be calm as the verdict was announced, while a jubilant Sulistyaningsih, clad in a black t-shirt with her face and the word "justice" emblazoned on it, hugged activists.

"I hope they will start treating migrant workers as workers and human beings, and stop treating us like slaves," she told a news conference after the verdict.

She called for reform in Hong Kong, and said her native Indonesia must not shirk its responsibilities to protect its citizens who travelled abroad to work.

Sulistyaningsih said that while she forgave Law, she hoped her former employer would receive the greatest possible sentence, "even though for me, that is still not enough compared to what she did to me and other victims."

- 'Justice upheld' -

"For me, personally, she should receive life imprisonment for what she did, and for the fact that she does not have any remorse for past actions."

"Justice must be upheld."

During the six-week trial, prosecutors said Law turned household items such as a mop, a ruler and a clothes hanger into "weapons" against her maids.

Sulistyaningsih has described in vivid detail how she was "tortured", starved, beaten and ritually humiliated by Law, with prosecutors saying she was treated as an "unpaid slave".

"It's a victory for Erwiana," Aaron Ceradoy, programme coordinator for the Asia Pacific Mission for Migrants, told AFP.

"It would be good if the migrant community can use this case to strengthen their position on their demands for changes in policies."

The case sparked protests by migrant workers in Hong Kong, and has thrust the plight of migrant domestic helpers in Asia and the Middle East into the headlines after other shocking incidents of torture and even killings.

Sulistyaningsih said she lived for months on nothing but meagre portions of bread and rice, sleeping only four hours a day and being so badly beaten by her employer that she was knocked unconscious.

Law's defence accused the former maid and another two domestic helpers involved in the case of being "opportunistic", and that the injuries could have been caused by accidents. Woodcock in her ruling dismissed those claims as "desperate and fanciful".

"The message should be brought home that if you live in a society where you're fortunate enough to employ a domestic helper, they're still protected by the law," police detective superintendent David Cameron told reporters after the verdict.

Hong Kong is home to nearly 300,000 maids from mainly Southeast Asian countries -- predominantly Indonesia and the Philippines -- and criticism from rights groups over their treatment is growing.

Amnesty International in 2013 condemned the "slavery-like" conditions faced by thousands of Indonesian women who work as domestic staff and accused authorities of "inexcusable" inaction.