Over one million revellers are expected to attend Notting Hill Carnival over the next two days.
The biggest street festival in Europe will feature Caribbean culture, food, music and dance in west London.
The event gets under way today with children's day and forecasters predict conditions will be dry but cloudy with temperatures up to 19C.
Flamboyant costumes and thumping basslines will fill the air as giant floats make their way from Westbourne Park Underground station to Ladbroke Grove.
Organisers said this year marks the first milestone in the build-up to the event's 50th anniversary in 2016.
The arenas will pay tribute to the steel pan, the national instrument of Trinidad and Tobago which has played a pivotal role in shaping the carnival from 1964 to the present day.
The London Notting Hill Carnival Enterprises Trust acknowledged that some people believe the first carnival took place in 1964, while others say a "tentative" street parade with music and dance took place the following year.
But the organisation concluded that "documentary evidence" shows the first event with performers, costumes, music and placards occurred in 1966.
London mayor Boris Johnson said: "Carnival is a wonderful celebration and highlights what the Caribbean community does for London.
"This year there are two things which make it even more special - the 50th anniversary of steel pan and the free app which will guide you around the carnival route. I hope everyone has a fantastic time and a truly great event."
A number of business owners and residents have boarded up their properties on the carnival route in a bid to avoid damage.
A gang crime crackdown in the run-up to the party has seen dozens of arrests and the seizure of guns, drugs and thousands of pounds in cash.
Scotland Yard teams staged a series of dawn raids on Thursday, arresting 126 people by the late afternoon and retrieving weapons, including two machine guns and a handgun, crack cocaine and around £78,000 in cash.
Several of those arrested and released on bail will be banned from the carnival, with officers known as "super-recognisers" primed to spot them in the crowds if they do break the rules and turn up.
Chief Superintendent Robyn Williams said: "We are committed to ensuring that Notting Hill Carnival remains a safe, vibrant and enjoyable event.
"(The) operation was aimed at ensuring that those who set out with the intention of causing trouble at carnival will not succeed. By once again using our team of super-recognisers, we will quickly be able to identify and remove anyone prohibited from the event.
"If you know anyone who is planning to use Notting Hill Carnival to commit crime, please call Crimestoppers anonymously to help us keep the event a safe celebration."