With so much new music veering towards the small-scale - if not, in some cases, almost the aphoristic - one has to admire the somewhat alternative approach taken by a composer such as the Tan Dun (right). Born in China in 1957, he studied at the Beijing Conservatory when it opened in 1978 after the Chinese Cultural Revolution, but now makes his home in New York. And, in what definitely amounts to the biggest and longest of the UK premieres at this summer's BBC Proms season, Dun takes it upon himself to explode a few "little" issues such as heaven, earth and mankind, which, in fact, form the subtitle of his massive Symphony 1997.

That said, the work did not come about in usual commissioning circumstances. It commemorates no less an event than the reunification of Hong Kong with China, and was premiered in the city on July 1 only last year among ceremonies marking that transfer. In what amounts to a postmodern musical montage, Dun tries to evoke both a large-scale background canvas and man's solitary quest to locate and position himself against the same. Though by no means programmatic in nature, the solo cello part, written for Yo-Yo Ma, represents the individual voice of a storyteller rising out of, and ceding back into, the multitude.

Yet aside from his large symphony orchestra, Dun calls on two other sets of guest performers - a children's choir, proclaiming hope in the future; as well a massive set of ancient Chinese bells. In 1978, excavations at the tomb of Marquis Yi of Zeng uncovered 65 bronze bells that had lain buried since the fifth century BC. This set of bells is collectively known as "bianzhong", and spans an incredible five-octave range. In a sense, Dun's audacious employment of these ancient instruments therefore also renders his symphony a simultaneous concerto for cello, bianzhong. and orchestra.

Like the city of Hong Kong itself, Dun's vast and colourful score attempts to unite the cultures of East and West. An array of yin- and yang-like contrasts are evoked in everything from overall layout to individual timbres. A Taoist structure further imbues the symphony via its division into the almost Dante-esque spheres of heaven, earth and mankind. What results is a truly "global" concoction, by turns celebratory, pensive, spiritual and secular.

In Monday's alluring Prom, Jerzy Maksymiuk conducts the BBC Scottish Symphony Orchestra in a no less probing symphonic opus - Vaughan Williams's Symphony No 5, itself composed during turbulent historic circumstances in the darkest years of the Second World War. After the interval, under Dun's own baton, the orchestra has a very different symphonic territory to negotiate, when, along with Yo-Yo Ma, the New London Children's Choir and the forces of the Imperial Bell Ensemble of China, they evoke Heaven, Earth, Mankind in a 70-minute span.

Of course, such all-sweeping symphonic statements have been made before - Beethoven's Ninth and the essays of Gustav Mahler immediately spring to mind. Can Dun's ambition and inspiration match theirs? Whatever the ultimate merits of the score, this promises to be a very unusual musical experience.

Royal Albert Hall, Kensington Gore, SW7 (0171-589 8212) 3 Aug, 7.30pm