HONG KONG • Each Sunday, a choir of Filipino domestic workers in Hong Kong gathers to sing songs that remind them of the children they left back home.

Known as the Unsung Heroes, these initially shy singers now regularly perform around Hong Kong and feature in a new film on the lives of the city's domestic maids.

The theme of maternal sacrifice runs through the documentary titled The Helper - many domestic helpers are mothers working their way out of poverty, looking after other people's children to improve the lives of their own kids.

In an empty kindergarten classroom on a Sunday afternoon, the choir races through a series of crowd-pleasers, from Katy Perry's Roar to Bob Marley's One Love. But the songs they know best were written especially for them - their signature ballad Kiss You Goodnight tells of a wish to be with a child to put them to bed.

Ms Analyn Tapil, 49, wipes away tears as she recalls how she left her two sons, one just four months old, the other a year and seven months, over 20 years ago to earn a better living in Hong Kong. "It is a very big sacrifice to leave your children but I didn't have a choice," says Ms Tapil, who sent most of her pay home to fund her sons' education.

Now grown up, they have graduated and are working. "My children are a success," she says with a smile.

In a city of 7.3 million, there are more than 300,000 domestic workers, most of them from the Philippines and Indonesia.

Ms Jane Engelmann, head of performing arts at a Hong Kong primary school, launched the choir three years ago. Anyone in the migrant community can join, but Filipino helpers make up its membership of around 40 singers.

The film will be screened at one of the city's main central cinemas this month and in Singapore. A soundtrack will be available on iTunes and Spotify.

AGENCE FRANCE-PRESSE