Up to 200,000 people, many of them children, began the three-mile carnival parade which has become as much a part of the Bank Holiday festivities as rain and traffic jams.
Two million people are expected to attend by the time the event winds down tonight, watched by 3,800 police officers.
Stephanie Harwood, the spokeswoman, said many local residents were taking part this year instead of moving out for the Bank Holiday. She added: "Lots of people who live in the area are amazed to find how many friends they have as carnival weekend approached."
Rain stayed away from the festival but parts of Britain will not be so lucky today. A Meteorological Office spokesman said rain would sweep into Northern Ireland, Scotland and western parts of England and Wales, with fresh winds over much of the country. Temperatures hit 23C in Bristol yesterday.
Motorways were uncharacteristically quiet but AA Roadwatch warned of inevitable delays today. Among return travellers will be 130,000 people who spent the weekend at the Reading Festival listening to bands including New Order, the Beastie Boys, Prodigy and Supergrass.