Grizzly Bear, Barbican, London

Halloween night at the Barbican. Black-clad members of the London Symphony Orchestra take up their positions as dry ice billows over them. Ranged across the front of the stage, in among the waiting guitars, electronic paraphernalia and other instruments, are six T-shaped gantries, from each of which hang six glass jars. The effect is startling, and not a little spooky. But are these 36 jars there to be played? Or are they purely for decoration?

Anything seems possible with Grizzly Bear, the Brooklyn four-piece whose post-Radiohead sonic vistas have been blowing many a mind lately, and by the time they come on it is clear that this is going to be no ordinary gig. This is an Event. And what followed over the next couple of hours was of such sweeping scale and mysterious beauty as to fully justify the anticipation that was in the air.

Bringing in a symphony orchestra as your backing band is a bold move, and the enhancements provided by the string section were heart-stopping. Then again Grizzly Bear – four serious young men, including a besuited and bow-tied drummer, Christopher Bear, who seemed to have stepped out of the pages of an F Scott Fitzgerald novel – are almost a symphony orchestra in themselves. What they create – psych-folk, to give it a less than adequate label – are not so much songs as movements, ever-evolving rivers of sound with themes, variations, and recapitulations, but not always a resolution. The balancing of opposite was very fine: opulence and restraint; the cerebral and the stirring; experimentalism and order.

Along with the gorgeous lead vocals shared by Ed Droste and Daniel Rossen, and the equally striking falsettos of Bear and bassist Chris Taylor, Grizzly Bear depend for their effects on the most exquisite detailing, doodles of apparently random sound that come in and out of focus, forming an interlude here, a tributary there. It all adds up to music that seems to have been brought back from a planet whose civilisation is at a rather more advanced stage than our own.

Of the 15 songs the band performed, 10 came from this year's release, Veckatimest, which is surely destined to be many people's album of the year. "All We Ask" and "Foreground" were marvels of spaciousness and spiritual questing. "Two Weeks" was madrigal-like in its harmonic richness.

And the glass jars? They turned out to be lights. They twinkled and glowed, and flashed on and off to provide another magical touch on a night when everything Grizzly Bear did cast a spell.

Touring to 6 November (www.myspace.com/grizzlybear)