Every armed police officer in London will be deployed to help patrol New Year's Eve celebrations, amid a warning that European capitals were at risk of a terror attack.
There was no specific information that London was being targeted.
"Our plans are purely precautionary and not as a result of any specific intelligence," a Metropolitan Police spokesperson said.
The Telegraph reported that Scotland Yard had canceled leave for more than 2,000 armed officers -- the first time it has taken such a step for New Year. It has happened before for events such as the 2012 London Olympics.
Austria earlier this week said a "friendly intelligence service" told them that European capitals were at risk of getting attacked, without specifying which ones. European capitals were stepping up security and canceling fireworks celebrations, in some cases.
Police in Brussels arrested six people on Thursday in connection with an alleged plot to attack the city on New Year's Eve, and Turkish security services said they thwarted a plot to attack Ankara.
In London, Mayor Boris Johnson urged people to get out and celebrate.
“From our fantastic fireworks on the banks of the Thames to thousands of events in pubs, clubs and restaurants across the city I'd urge Londoners and visitors alike to get out there and soak up the best we have to offer," he said. "As with any other major event in the capital our policing response will be appropriate, but I'd stress we've seen nothing to suggest a specific threat to London.”
Morning folks, it’s not long until #LondonNYE. Here are my tips to help you have a great night, whatever you do https://t.co/P82l4Ol0oH— Boris Johnson (@MayorofLondon) December 31, 2015
More than 100,000 people are expected to turn up to see the fireworks in London, which is a ticketed event.
Ken Marsh, chairman of the Metropolitan Police Federation, said: “I think people will defy the terrorist threat. Londoners are very resilient and have a lot of faith in their police officers to keep them safe.”