Hong Kong's top court on Tuesday began a hearing to decide whether the hundreds of thousands of domestic workers who make a living in the Asian financial hub are eligible to seek residency.

The case, brought by Filipina maid Evangeline Banao Vallejos, could also reopen the controversial issue of whether children born in Hong Kong to mainland Chinese parents have the right to stay.

Vallejos won a High Court ruling in 2011 granting her the right to request permanent residency status, denied to foreign maids until then.

The government appealed against that ruling last March, successfully arguing the authorities had discretionary power to decide who was eligible for residency and that restrictions on maids were not unconstitutional or discriminatory.

Hong Kong's 300,000 foreign maids receive a minimum wage of HK$3,920 (US$505) a month and benefits such as one guaranteed day off a week, but rights groups say they face discrimination and a lack of legal protection from abusive employers.

Campaigners argue they should not be treated any differently from other foreigners who flock to the former British colony to seek professional work and who are eligible to apply for permanent residency after seven years.

"If you have a purpose that is regular and your presence is lawful and your presence is here for seven years continuously... and there has been no discontinuity, you would expect to succeed," Vallejos' lawyer Michael Fordham said in court.

The hearing in the Court of Final Appeal is expected to last up to three days but a decision may not be handed down for some time.

Government officials have warned that making domestic helpers eligible for permanent residency could open the floodgates to hundreds of thousands of residency requests from maids, some of whom have lived in Hong Kong for decades.

The case has also highlighted the issue of the city's judicial independence from Beijing, as it could potentially reopen the issue of whether the children of mainland Chinese parents can stay in Hong Kong.

The government has said the case should be referred to Beijing for its reinterpretation of the Basic Law, the mini-constitution which sets out the city's semi-autonomous status and rights since its return to China in 1997.

If that were to happen, Beijing would also need to decide on the status of children born to mainland Chinese parents who weren't permanent residents at the time of their birth, according to Basic Law expert Professor Lin Feng.

Lin said the government's request to the court "puts the judiciary under pressure, but they can say no and we don't need to seek clarification".

In 1999 the Court of Final Appeal ruled that children of people who have right of abode also have that right, even if their parents were not permanent residents at the time of their birth.

Hong Kong's government asked Beijing to "reinterpret" the Basic Law after claiming an extra 1.6 million people in China could obtain the right of abode, causing a severe social and economic strain on the densely populated city.

Beijing subsequently ruled that children born outside Hong Kong were only eligible for right of abode if at least one parent was already a permanent resident.

However, in 2001 the Court of Final Appeal ruled that children born in Hong Kong to mainland parents had right of abode regardless of whether their parents were legal residents.