Björk, Apollo Hammersmith. London

This is planet Björk

One downside of Björk's childlike aura - she hops around the stage like a tot buzzing on Sunny Delight - is that it prevents some critics from taking her seriously. Factor in the usual "nutty Icelander" stereotype, and it's not hard to see why her music has sometimes been overshadowed by media caricature. Unfortunate, that, because Björk Gudmundsdottir, now 37, has long been one of pop's most gifted and innovative songwriters. Tonight's gig at the Apollo, moreover, proves typical of a chanteuse for whom envelope-pushing has become the norm.

The DJ warm-up set does not augur well. Featuring ear-piercing animal shrieks, verbal abuse and other aural irritants on a par with a pneumatic drill, it's booed and slow-handclapped when rare dips in volume allow. Some kind of Björk-sanctioned prank? Perhaps. It also ensures that whatever comes next will be a welcome alternative.

Initially, at least, Björk's set is a sharp sonic contrast. Joined by the San Franciscan electronica duo Matmos, the harpist Zeena Parkins and an Icelandic string octet, she begins with "Pagan Poetry", the haunting stand-out track from 2001's Vespertine album. A ballerina-like figure in a red puffball dress and pink tights, Björk takes her usual aerobic approach to singing. Pumping her arms and legs to propel her honeyed bark on the song's outro section, she barely seems to require the microphone's assistance.

"Desired Constellation" is the first of three songs from Björk's forthcoming record, The Lake Album. "It's tricky when you feel that someone has done something on your behalf," she sings. The lyric's syntax is recognisably Björkian, and its starting-point is typically intriguing. The sonic backdrop is a thrumming electronica groove, but there is also a video backdrop, the first of several Lynn Fox visuals commissioned to enliven tonight's performance. This one features a distant galaxy and porpoise-like creatures with human hands for tails. Quite what it all means escapes me, but aesthetically it's highly pleasing.

This is the opening date of a European tour, and there are a few minor hiccups. For example, the manually triggered beats in "Joga" (designed to evoke Iceland's physical geography, they pay crunching homage to tectonic plates shifting) are out of time, and the string octet is sometimes lost in the mix. Björk herself is outstanding, though, her aura of other-ness and gung-ho enthusiasm holding our attention throughout. Other than, "Thanks", she says little between songs. This being Eurovision night, however, she does ask whether anyone has heard the result.

For "Nameless", the "psychedelic chamber-techno" artist Leila Arab arrives to effect a ghostly live remix of Björk's vocal, before the set-closers "Where is the Line" and "Pluto" up the tempo and sonic intensity. The former melds a distorted flamenco-like vocal to a monster groove, while the latter is bolstered by the kind of flame-throwing pyrotechnics normally associated with the Seventies hard-rockers Kiss. Having enjoyed a little head-bang, Björk receives a deafening ovation. "Angleterre - douze points!" she shouts; then the Sunny Delight kicks in again, and she's gone.