The 100-plus member orchestra will be performing in Macau and Beijing for the first time, returning to Hong Kong and Shanghai after six years, and playing in Taipei and Tokyo after an even longer hiatus. This tour has been four years in the planning, and is the tent-pole event for what is arguably one of the world's finest symphony orchestras.

Speaking at a morning event at San Francisco's Louise M. Davies Symphony Hall, the ensemble's home, a few weeks before starting the tour, Tilson Thomas describes the popularity of Western classical music in Asia as "a phenomenon".

"During my lifetime, I've seen it change enormously, and I've tried to understand what it is about the music that makes it as popular as it is," he says.

His deduction? "The virtuosity and athletic aspect of the music, a demonstration of many people's abilities to co-operate together to make something expressive, and also what the music itself expresses - the territory of thinking that the music represents in its long history. It's a mixture of many pleasures."

The two Hong Kong performances, on November 8 and 9, will present a different repertoire each night. The first will feature star pianist Yuja Wang as soloist on Prokofiev's Piano Concerto No2 in G minor, followed by the Symphony No2 in E minor by Rachmaninov. The next night the orchestra will play pieces by American composers Henry Cowell and Lou Harrison, concluding with the rousing Mahler Symphony No5 in C-sharp minor.

"It's an interesting mixture," Tilson Thomas says of the programmes. "It's a combination of the music that we do at home, and also the music that various hosts and presenters in the different countries want to hear. We are known for doing quite an adventurous repertoire."

Wang, who will appear in all of the Asian countries the symphony is travelling to, is something of a protégé of Tilson Thomas, who is a brilliant pianist in his own right. He first heard her several years ago when she was starting out. "I was told she was extraordinary and I came to a rehearsal for one of her performances," he says.

"What was so amazing was not just her virtuosic playing, but how well she knew the music - the orchestra was playing, every instrument. She was amazingly sensitive. That very much impressed me. It's unusual for a young pianist to have that."

Tilson Thomas and Wang have collaborated numerous times since then. "She has immense imagination, immense energy," he says. Typically, even after one of their performances, Tilson Thomas says he and Wang will get together to talk for an hour or so about the pieces just played. "This is my own approach to my own way of making music. It's always changing, never staying still, always evolving. She has that kind of spirit."

John Kieser, the symphony's general manager, says the group has been "overwhelmed with invitations" to play at Asian concert venues. He recalls a visit to the Shanghai Conservatory in 1987, during a particularly cold day, which gave him a sense of just how much the students loved what they were doing.

"There was not a lot of heat in those buildings, but the dedication of those young people practising both Western and Chinese instruments was obvious. It did not matter that they were cold; they were really passionate about their music," Kieser says. "That resonated with all of us - this is where we can come together with our passion for music and join with theirs."

To that end, some of the time on tour will be put towards connecting with musicians and music students in Asia.

Tilson Thomas is confident that Asian audiences will respond to the selection of music as enthusiastically as Americans have. The music director has a particular affinity with Gustav Mahler, and has seven Grammy awards for recordings of Mahler's music to prove it. He recalls meeting the late composer's widow, Alma, in a bookstore in Los Angeles when Tilson Thomas was 11 years old.

"She flirted with me," he says, smiling, mimicking the late socialite's noble European mannerisms. "For one fleeting moment I got the impression of just how seductive she was, and maybe a little of that can still be heard in this performance I'm doing in her honour."

Still, Tilson Thomas is known for more than his avant-garde approach to classical music. He considers every instrument in the orchestra as its own entity. With an imaginative repertoire and musicians who are allowed to shine individually, the symphony is one of its home city's greatest assets, routinely selling out performances.

"The work I've done with the orchestra is to go in the direction of content, colour, inflection, to give the soloists and the different sections of the orchestra the opportunity to make the music very focused as far as its expression and intention is concerned," he says.

"I like to let them feel as if they have the same freedoms they will have if they are playing solo or chamber music."

And the fact that Tilson Thomas likes to spotlight unusual works, such as the two American opuses before Mahler's Fifth, has become one of the symphony's signatures. "It's an opportunity to take great risks and reach the public with the message the composer left for us," he says.

The music director routinely receives letters and e-mails from audience members asking why he presented a piece of music that they might describe as "unusual" or "challenging". He writes back, he says, asking them "to imagine that we were on an ocean voyage and suddenly came across an island that was completely uncharted, no map had ever reported this island existing. And when we take out our binoculars and look out to shore, there are all sorts of animals and plants that were never described before. Wouldn't that be thrilling, and the best possible thing that could happen to you?

"I tell them that's why I did this piece of music, because it has no relationship to anything anyone ever knew before. You discover something completely new, you expand your experience, it's something you can talk about. That's one of the things I think a night at the concert hall should always be about."