Every available officer at the Metropolitan Police's disposal will be on duty tonight - including hundreds of specially trained firearms personnel.
Scotland Yard said there would be around 3,000 officers across central London as mayor Boris Johnson's fireworks display with Unicef brings in 2016.
The Met confirmed New Year's Eve was one of two events - along with Notting Hill Carnival - in which there was no holiday entitlement, meaning all available staff were called upon.
It comes at a time of heightened security in capitals across the world in the wake of the Paris terror attacks.
Metropolitan Police spokeswoman Superintendent Jo Edwards said: "Around 3,000 officers will be on duty as part of our policing operation for the central London fireworks display, to play our part in ensuring that people see in 2016 safely.
"Across London my colleagues will be on duty providing our usual policing service.
"I hope that everyone in the capital has a safe and enjoyable New Year's Eve.
"Whilst we do not discuss numbers of armed officers on duty, contrary to some media reports officer leave has not been cancelled.
"Every year officers are rostered to work New Year's Eve and Notting Hill Carnival as these are major policing operations in our annual calendar of events. This year is no different.
"We will be working closely with our partners at British Transport Police who will have additional armed officers in and around central London transport hubs throughout New Year's Eve."
The London event takes place as the New Year's Eve fireworks display in Brussels is cancelled because of threats of an extremist attack.
Brussels mayor Yvan Mayeur said the decision was taken on Wednesday evening after consultation with government officials.
Last December 31, 100,000 people turned out in the Belgian capital to ring in the new year.
Brussels was home to four of the radical Islamic attackers who killed 130 people in Paris on November 13.
The Metropolitan Police said it had been working closely with the mayor's office, British Transport Police (BTP), Westminster City Council and others to ensure the event ran smoothly.
The mayor's fireworks display was ticketed for the second year and has sold out.
On New Year's Day, more than 8,500 performers representing 20 countries will take part in an annual parade through London.
The event, which includes marching bands, cheerleaders, clowns and acrobats, kicks off in Piccadilly and finishes in Parliament Square, taking in Lower Regent Street, Pall Mall, Trafalgar Square and Whitehall.