And Chung, 54, is delighted they're helping to liven up Hong Kong's streets, which he describes as 'a bit too cold'.

'Playing on the streets is challenging, because you have an audience which hasn't come to see you,' he says. 'Hong Kong people are known for their fast-paced life, but if they are prepared to slow down, listen to us play and applaud, it's a great encouragement.'

Yung, a former police sergeant, had signed up for classes as diverse as yoga and Cantonese opera after retiring 10 years ago, but he found an enduring passion for jazz after joining the instrumental course. Organised by music school Orchestre de Joie, the seniors' course has attracted more than 100 people since it began in 2007.

'Most participants in classes at elderly centres are women, so it's hard for me to get involved and open up,' says 63-year-old Yung.

'But in this class, most of the participants are guys and we have more things in common.'

Their street adventures started, however, after Chung accepted an invitation from his alma mater, Wah Yan College, to perform at a fund-raiser last November. He may have been the daring whistle-blower who warned Sars was spreading beyond hospitals in 2003, but Chung was thoroughly intimidated when he started rehearsing with his fellow alumni. 'They played so much better than me. I couldn't even blow a few notes, I was so nervous. But it was too late to pull out,' he says.

To help Chung overcome his nerves, Yung suggested he warm up by performing before street crowds. Now, the semi-retired surgeon sometimes even strikes out on the pavement by himself.

'One guy even dropped me a dollar coin when I played on Portland Street,' Chung says with a grin. Occasionally passers-by introduce themselves, among them former patients or students. 'They appreciate my courage to play on the streets and in subways even though I don't play well.'

The group have also performed for patients at the Haven of Hope and Pok Oi hospitals. But as much as they enjoy entertaining the community, nothing beats the spontaneity of street performances, Chung says.

Their repertoire of golden oldies - tunes such as Moon River - were pop hits when they were teenagers and 'playing these songs makes me feel young', says Tony Ching, a former civil servant. 'Besides, I feel cool carrying a saxophone around on the street - as if I were an ancient warrior with a sword on my back.'

Their impromptu concerts have been an inspiration for Katherine Mak Kit-yin. The 24-year-old merchandiser came across the band last December as they played at the promenade outside the Cultural Centre and followed the musicians to a nearby subway after they were expelled by a security guard.

'I'm impressed,' she says. 'Hong Kong isn't known for street performances. It's so unusual to see a group of people play saxophones. Most buskers are soloists.'

Mak says their playing has reignited her passion for music. She played the saxophone as a student and has now been encouraged to take up the instrument again.

Mak joined the group over the Christmas period for subway shows in Tai Po, Tai Wai and Sha Tin ('We like the reverberation in the enclosed space,' Chung says).

Their music attracted plenty of revellers, some of whom thanked them for enhancing the festive spirit. 'The atmosphere was great and many people came to talk to us afterwards,' Mak says.

Besides their weekly practice after classes at the Cultural Centre, a few members hungry to make more music rent a studio in San Po Kong for a big-band-style session on Thursday evenings.

Former civil servant Keith Tsui Yuk-kwan, who initiated the Thursday sessions, welcomes the chance to express himself. 'We are less accomplished technically but we definitely have a load of emotion because of our life experiences,' the 57-year-old says.

Their saxophone teacher, Yau Kin-chung, admires their dedication. His students take longer to perfect a small move because their fingers are less nimble due to age. Even so, Yau, a former member of the British army's brass band, says he takes great pride in their progress.

For their part, the amateur saxophonists can't thank their families enough for putting up with the noise as they learned to play their instruments.

Chung started learning to play music during a stint in Papua New Guinea as professor of surgery at Port Moresby General Hospital. Stopping for drinks after work, he began learning the trumpet from Filipino bands playing in pubs. By the time he started playing sax after returning to Hong Kong, his wife and daughter would complain because he played badly. 'Even my dog barked when I played,' says the surgeon, who now spends his time playing sports, fishing and taking an occasional consultancy.

But as their playing improves, the jazz musicians are regularly requested for family gatherings. Last year Chung's daughter got him to play at her friend's birthday party. 'My daughter is proud of me now,' he says.

Chung's enthusiasm seems to have spread to his neighbours in Shek O. 'They hum the songs I practise,' he says. 'First, it was the theme from The Godfather. Now it's Cherry Pink.'

Encouraged by friends and his teacher, Yung found music to be a superb present to his wife on their 40th wedding anniversary: he serenaded her with The Moon Represents My Heart, by the Taiwanese singer Teresa Teng Li-jun. 'It's embarrassing for me to thank her in words, so I let the music speak for me,' Yung says.

His wife, Amy Yuen Wai-king, loved it. 'He's become more romantic since he started learning the instrument,' she says. 'I enjoy seeing him absorbed in music.'

Ching has found a supporter in his teenage son. 'My son didn't believe I had the nerve to play on the streets, so he came to check me out,' Ching says. 'Since then, he has come along to help me carry the instrument and take photos.'

Keen to share their favourite songs with more people, Six Sax & Horn hope to stage a show from the upper deck of a tram. But they know they have to put in a lot more work polishing their performances.

'I feel like a student who has switched to a class using English as the medium of instruction,' says Chung, wiping sweat from his forehead after a lively lesson. 'As you get older, it's harder to pick up a new skill. But nothing is impossible as long as you're persistent.'

Students from Orchestre de Joie's seniors class will perform on Sunday as part of an RTHK concert to mark the 60th anniversary of the People's Republic of China, 2.30pm, City Walk mall, Tsuen Wan.