Clad in blue and yellow prison uniforms, about a dozen prisoners sang and played instruments as they performed their song, Have a Happy Christmas, at the prison's hall.
Two leading members of the group, known as "Ah-Nam" and "Ah-Kei", aged 35 to 45, are serving life sentences. They wanted to help the fundraising campaign launched by the Child Development Matching Fund.
Their song will be performed at concerts held at public venues across Hong Kong, including theme parks and shopping centres, until Christmas Eve.
The community-based fund, launched in 2010, raises money to give support and development opportunities to thousands of children, aged 10 to 16, from disadvantaged families.
Last year's Carol Singing Festival raised more than HK$2 million.
Ah-Nam wrote the music and lyrics to the upbeat song. Songwriter Mahmood Rumjahn - better known as Lam Miu-tak, who produced many iconic Cantonese records in the 1980s - volunteered to produce the song for the band.
It took Lam and the prisoners only a week to rehearse and record the song, long enough for Lam to be impressed by the inmates' talents. "They're trying their best to put their past behind them and are eager to show their talent to everyone out there," Lam says.
Most of the band members have little or no musical background. Both Ah-Nam and Ah-Kei took up music after entering prison.
"As a reward for good behaviour, I started playing music in the band in 1998," says Ah-Nam. "Before that, my contact with music was limited to karaoke."
He and Ah-Kei praised the government's Correctional Services Department for helping to provide volunteers from Hong Kong Sinfonietta and Hong Kong Academy of Performing Arts to help teach them music theory.
"The volunteers didn't mind our background and the love and support they showed us was immense," Ah-Nam says.
"So we felt that we needed to do something in return for people outside prison."
He says his Christmas song reminds him of happier days when he was a free man.
The melody and lyrics were inspired by letters from his loved ones.
"Family letters can change our routine life in prison," Ah-Nam says. "Sometimes I just can't fall asleep after reading them; writing songs helps me to express my feelings.
"It feels strange when you are separated from your loved ones and are trying to imagine the festive atmosphere outside ... but you have to bear the consequences of your choice in life."
Ah-Nam is not alone among the band members in writing songs: everyone contributes songs, even though they don't have musical instruments in their prison cells.
"When inspiration comes, I usually start by humming tunes and write them down using words that sound similar," Ah-Nam says. "Then I wait to fully create the song at our weekly practice."
The fund's director, Amy Chan Kung Wai-ying, praised the efforts of the inmates.
"Although they have no musical background and only two or three hours of practice each week, it is amazing to see what they can do with their talent," she says.
Shek Pik Prison