Hundreds of thousands of revellers will descend on the Notting Hill Carnival over the next two days for Europe's biggest street festival.
Scores of costumed masquerade artists will join steel drum bands to perform along the three and a half mile route through west London.
A change to this year's event will see the carnival procession begin at the earlier time of 9am and end at 6.30pm both today and tomorrow.
London mayor Boris Johnson said: "Notting Hill Carnival is the summer celebration that attracts visitors from across the globe to London for the ultimate free street party.
"This year I encourage you all to arrive early to enjoy the colourful floats and the sounds of the massed bands and steel pans.
"The historic event highlights the best of Caribbean culture and the contribution that Caribbean Londoners have made.
"It illustrates the energy and colour of our great city, which is woven into the fabric of London life.
"There really is no better place to sample delicious Caribbean food and enjoy the dazzling colours of the costume parade. I hope everyone has a truly wonderful time at the carnival this year."
Ch Insp Jo Edwards, of the Metropolitan Police, said: "Carnival is a wonderful, unique and vibrant event, which is of great importance to London.
"Our job is to make sure we do all we can to keep the thousands of people who go as safe as can be.
"Given the huge number of people who take part in Carnival, crime rates are low, and our policing style last year made sure that less people were a victim of crime.
"We will be working with the full support of the organisers and the community to ensure that success continues this year."
Police have already said there will be a major security operation around the event.
Officers will man a series of security rings to target known troublemakers and flush out anyone carrying guns or knives.
More than 150 people have been sent letters telling them to stay away and 16 suspects have been arrested in the run-up to the event.
Since August 17, police have held suspects across the capital for possession and supply of Class A and B drugs including cannabis, handling stolen goods and breach of an ASBO.
More than 60 rocks of crack and a quantity of cannabis have been recovered, along with two samurai swords and a butterfly knife, goods such as mobile phones and laptops believed to have been stolen and £2,000 in cash.
Officers have also carried out regular stop and search operations to disrupt gang activity, in areas where there is intelligence that gangs may attend Carnival.
These have led to a number of arrests and a car has also been seized for having no insurance, Scotland Yard said.
The force is also warning people to leave dogs at home as they team up with the RSPCA to stop them from being taken to this year's event.
Officers from the Met's new Status Dogs Unit will be staging an operation to seize suspected dangerous dogs.
Last year officers from the Met's Dog Support Unit seized 20 suspected pitbulls and sent 120 people with dogs away from the area.Reuse content