Hundreds of children paraded through the streets as the first day of the Notting Hill Carnival got under way.
Police numbers were increased in an effort to prevent trouble in the wake of this month's riots in London and by 20:00 BST Scotland Yard said 53 people had been arrested.
Carnival drew to a close 90 minutes earlier than usual, at 19:00 BST and is due to end at the same time on Monday.
In both 2009 and 2010, there were more than 200 arrests across the two days.
The Metropolitan Police deployed 5,500 officers on Sunday, with 6,500 due to work on Monday at what is thought to be Europe's biggest street festival.
Hundreds of thousands of spectators watched more than 30 floats on the route along Ladbroke Grove and Westbourne Grove.
Crowds built up "steadily at anticipated levels", police said.
Officers searched some people in an effort to "stop weapons getting into the carnival".
This was "to keep people safe and take weapons off the streets", said Commander Steve Rodhouse.
He added: "We've worked closely with event stewards and have seen huge support from all Carnival participants to meet that really important earlier close down.
"Looking ahead to tomorrow, we will have a larger operation in place. Our intelligence picture has not changed and we will make sure that our officers are out stopping the right people so everyone else can take part and join in the fun."
Some roads and Tube stations have been closed for the carnival and Transport for London has issued a guide with full details.
One of the event's directors, Ancil Barclay, said it was important to show that the violent image of London, seen during the riots, was "really not applicable" to the city's Caribbean community.
"I would invite everyone to come out and look at the amount of young people we have in the streets of London, showing off their excellence in different forms," he told BBC Radio 5 live.
On what is the festival's children's day, youngsters sprayed themselves with brightly-coloured paint and powder as part of the messy J'ouvert celebration at the beginning of the first day of the carnival.
The table sauce entrepreneur Levi Roots said the Sunday of the festival was "fantastic" and was "always special".
"The most beautiful thing you will see on the street is these kids, dressed up in the costumes."
It is expected more than a million people will attend the event over the two days.