Florence and the Machine, Bloomsbury Ballroom, London

On a stage littered with floral arrangements, in almost complete darkness, a solo drum beats repeatedly until a figure eerily emerges, draped in a floaty beige dress. She brings her arms up and the sleeves fall into place like wings, a raven-haired bird-like creature standing in front of us. And then the voice comes. A series of ethereal, high pitched "oohs", which immediately give you goosebumps. She is Florence Welch and she's here to save you from the weary, stale and flat concert-going experience.

The singing dynamo has yet to release her debut album but is probably already surprised by just how much the mainstream has embraced her. The 22-year-old from south London was the winner of this year's Brits Critics' Choice Award, won last year by another girl with a big voice, Adele. She sung in various choirs growing up, started writing songs aged 13, before drunkenly singing to her now manager in a club toilet, and was thrust onto the live circuit.

Her macabre subject matter has garnered a lot of attention. The world she seems to inhabit is not life as we know it, but rather that of the Brothers Grimm... in outer space. After the opener "Between Two Lungs", she performs "Hurricane Drunk", "Girl with One Eye" and "Howl" in quick succession. Or as she charters it: "From drinking yourself to death, to cutting out a girl's eye to eating someone's heart."

Those who caught her earlier live shows or listened to her original songs posted online, and are familiar with a more folky, bluesy sound, may be surprised by the path that Florence has skipped down. Her camp has taken their time with her, experimenting with sounds and delving into different territories. Producers Paul Epworth (Bloc Party) and James Ford (Klaxons, Arctic Monkeys) have honed a completely original, eclectic noise that acts like a journey through soul music. On the album, Lungs, aptly named not only for her billowing voice but also her almost medieval preoccupation with body parts, we are treated to classic bluesy soul, disco soul, even Nineties vocal house music. The original raw and messy sound has been banished and replaced with something that is solid, gutsy, passionate and powerful.

Although, obviously, other strong experimental female acts such as Kate Bush and Björk have paved the way for her, there's little point in comparing her to anyone else, if for no other reason than she switches genres of music and style with ease, leaving it impossible to pigeon-hole her. "Kiss with a Fist" exposes her mighty voice and is guitar happy while "Dog Days Are Over" comes complete with harps, violins and clapping.

Probably the best song of the night is her upcoming single, "Rabbit Heart (Raise It Up)". It starts as some kind of Alice in Wonderland-set bohemian dance tune but by the time you get to the chorus it reaches epic proportions and you're in euphoric tribal, house music territory as she urgently belts out: "This is a gift, it comes with a price/Who is the lamb and who is the knife?/Midas is King and he holds me so tight/And turns me to gold in the sunlight". Live, it is helped along by Florence dancing crazily in front of a strobe light and it is quite a moment.

For most of the night, the audience don't really move, or dance. They are all transfixed at what is going on on stage. She hollers, twirls, struts, clambers on to speakers and dives into the audience. Her live show blows the other girls of 2009 out of the water, in terms of the calibre of songs and stage presence. But it is her voice that will really take Florence to the top. Those incredible lungs.