Crowds have begun to gather in central London ahead of the New Year's Eve fireworks, which are expected to be seen by up to 250,000 spectators.
The eight-minute display will have a musical soundtrack for the first time.
Victoria Embankment and Westminster Bridge have been closed to traffic and other areas will be shut as the evening goes on to prevent overcrowding.
Police have urged people to set out early and to take care of their belongings in the busiest areas.
"Don't leave it to the last minute to watch the fireworks, as you are likely to be disappointed," said Metropolitan Police Supt Julia Pendry.
"The viewing area is very popular and gets full early on in the evening."
She went on: "We want Londoners and all visitors to the capital to be able to welcome the New Year in a safe and crime free environment."'Character of London'
The organiser of the celebrations, James Donald, said the display would consist of "really high-energy fireworks".
He said BBC Radio 1 DJ Nihal had created a dynamic soundtrack of "cool tunes".
The show would really bring to life a bit more of the character of London than in previous years, Mr Donald added.
London Ambulance Service (LAS) staff are preparing for one of their busiest nights of the year, with more than 500 emergency calls an hour expected.
Deputy director of operations Jason Killens asked people to "use the ambulance service wisely and only call us in a genuine emergency".
"We'll be prioritising our calls and going to those with the most serious conditions first."
He said LAS did not "want to be killjoys" but stressed drinking alcohol "in moderation" was important.
"Don't call the ambulance service simply because you're drunk, when you're looking to go home."
Later on Saturday more than 500,000 people are expected to watch London's New Year parade, which is marking its 25th anniversary.