By Peter Griffiths

LONDON (Reuters) - Blowing whistles and dancing in the drizzle, thousands of revellers packed the streets of west London on Sunday for the first day of the Notting Hill carnival, one of Europe's biggest open-air parties.

Organisers said 1.5 million people from around the world were expected to throng to the two-day carnival of colourful processions, thumping sound systems and exotic food stalls.

The theme of this year's carnival, which coincides with the Olympic handover to London from Beijing, is "Welcoming the World". The crowds followed the closing ceremony in China on a giant 25-metre screen erected in the heart of the carnival.

London Mayor Boris Johnson, who is in Beijing, sent a message of support to the carnival, saying: "Nothing beats the sounds of the steel pans, the aroma of delicious Caribbean food and the dazzling colours of the costume parade."

Hundreds of performers covered in multi-coloured body paint, sequins and feathers danced through the streets to the thunderous sound of soca, reggae and steel bands. The sun was expected to break through the clouds later in the day.

Children in elaborate animal and bird costumes joined the parade on Sunday, traditionally a family day.

The carnival takes place in the fashionable west London area portrayed in the film "Notting Hill", starring Hugh Grant and Julia Roberts.

The smell of curried goat and spicy jerk chicken cooked on open grills filled the air. Hundreds of street stalls sold food from the Caribbean as well as Nigeria, Thailand and China.

Organisers said the crowds would munch their way through a tonne of rice and peas, 30,000 corn cobs and 15,000 fried plantains, washed down by 25,000 bottles of rum and 10,000 litres of Jamaican stout.

Police said they would use stop-and-search powers, metal detectors and dog handlers to create a "hostile environment" for criminals after a wave of knife and gun crime in London.

Police Deputy Assistant Commissioner Chris Allison said he was determined to stop weapons being used, and police arrested nine people before the event for firearms and drugs offences and possession of a banned dog.

Police want to stop people bringing dangerous dogs to the carnival after reports of dog fights at last year's event.

Inspired by the Trinidad Carnival, the Notting Hill carnival was first held in London in 1964 and has grown into one of the world's biggest, generating 100 million pounds ($187 million) for London's economy.