HONG KONG (AFP) - 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 Sulistyaningsih, 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.

"She was, for want of a better word, a prisoner on those premises," Judge Amanda Woodcock said, referring to Sulistyaningsih, who told the court she had been "tortured".

"I am sure the defendant did assault, wound, and threaten (Sulistyaningsih) as charged."

"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, who lowered her head but appeared to be calm when the verdict was announced, was found guilty of 18 of the 20 charges laid against her, including grievous bodily harm and criminal intimidation.

The only two counts she was not found guilty of were related to her treatment of another domestic worker.

She had denied all the charges, and faces sentencing on February 27, with a maximum possible jail term of seven years.

The charges against Law, who was arrested in January 2014, included grievous bodily harm with intent, assault, criminal intimidation and failure to pay wages.

A jubilant Sulistyaningsih, clad in a black t-shirt with her face and the word "justice" emblazoned on it, hugged activists after the decision was handed down. "I am very happy because I got justice from Hong Kong," she told journalists outside the courthouse, while thanking people for their support.

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," an ecstatic Aaron Ceradoy, programme coordinator for the Asia Pacific Mission for Migrants, told AFP outside the courthouse.

"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 shocking incidents of torture and even killings.

Sulistyaningsih said she lived for months on nothing but 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", saying their evidence showed the injuries could have been caused by accidents.

"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.

It found that Indonesians in particular were exploited by recruitment and placement agencies who seize their documents and charge them excessive fees, with false promises of high salaries and good working conditions.