Crowds of up to 100,000 are expected to gather in central London to see in the new year on Wednesday.
Trafalgar Square attracts tens of thousands on New Year's Eve
Police are preparing for large crowds in Trafalgar Square, Parliament Square and Leicester Square, despite no organised events.
An extra 3,000 officers have been drafted in - 500 more than last year - amid fears of a terrorist attack.
Scotland Yard is asking people to consider watching the London Eye fireworks display on television.
Assistant Commissioner Bernard Hogan-Howe advised anyone planning to head to central London to "think carefully beforehand".
He said: "Traditionally many people gather in central London to see in the new year, despite there being no attractions and no shelter from the harsh weather conditions.
"Substantial crowds do gather and this is not an appropriate environment for children or pets.
Roads and bridges shut
"This year the mayor has arranged a brief firework display to mark midnight. This will be televised live and you will be able to see it on a television wherever you are."
He added that while there was no "specific information" about a terrorist attack, he urged the public to be vigilant.
Trafalgar Square's fountains are to be cordoned off in an attempt to stop midnight dips.
And some roads and bridges will be shut to traffic.
The Tube, buses and trams will be free from midnight and underground trains will run until 0430 GMT on 1 January.