London welcomes 2009 with a spectacular fireworks show over the River Thames.
Millions of revellers around the UK have braved freezing temperatures to welcome in 2009.
In London, crowds started lining the banks of the River Thames hours in advance of the fireworks display.
They were played a series of video messages, from the likes of London Mayor Boris Johnson, actress Dame Helen Mirren and Homer Simpson.
Some 100,000 partygoers in Edinburgh watched fireworks and listened to live bands in sub-zero temperatures.
A range of New Year events also took place in Cardiff, Manchester and Birmingham.
About 400,000 people are believed to have gathered in London for the fireworks, while Elton John played at the O2 Arena.
Supt Brian Pearce, of the Metropolitan Police, said the revellers appeared to have heeded warnings to arrive early to get a good view of the show.
He said: "The viewing areas started to fill up at about six o'clock this evening."
Scotland Yard said it had made 78 arrests during the festivities in the capital, with about 3,300 officers involved in the Met's policing of the night.
Last year, as of 0400 GMT, more than 70 people had been arrested, the majority for public order offences or for being drunk and disorderly.
However, in the first hour after midnight this year the London Ambulance Service took fewer calls than last year.
A London Ambulance Service spokeswoman said: "Between midnight and 0100 we took 292 calls, compared with 377 in first hour of New Year's Day last year."
Partygoers waiting for the stroke of midnight in London were entertained by giant projections and light shows on the walls of the city's landmark buildings.
Many came equipped with wine glasses, thermos flasks and picnics.
The Hudson family, who had travelled from Nottingham for the event, sported flashing bunny ears.
Nurse Corinne Hudson, 47, explained that the family had planned the trip on New Year's Day last year when she was undergoing chemotherapy for ovarian cancer.
The Holmes family in Bristol welcomed the New Year in with a bang
She said: "My hair started falling out on New Year's Eve last year. So we spent last year crying.
"Watching it on the television everybody seemed to be having a good time here whilst we just weren't. So that's why we're here tonight to put that behind us and move on."
The crowd were played a series of video messages, beginning with an address from London Mayor Boris Johnson, in which he urged the city to "go forward with enthusiasm" into 2009.
Actress Helen Mirren told the crowd that despite the fact she was on the other side of the world, her heart was with "insane Londoners".
"And you've got to be insane, because I bet it's freezing," she said.
Veteran actor Michael Caine said he would normally wish for a "prosperous" New Year.
But instead he said: "This year I think what we really need is luck, so good luck everybody."
The party in Edinburgh - the self-styled Hogmanay capital - has been under way for a number of days.
Events included fireworks around Edinburgh Castle, live bands and a huge singalong of Auld Lang Syne, which organisers hope will break a world record.
A spectacular firework display heralded the start of 2009 in Edinburgh
In Cardiff revellers will be able to sleep off their partying in an inflatable tent staffed by medics at the Millennium Stadium.
The sleepover centre has been converted from an emergency chemical decontamination tent.
Sub-zero temperatures were forecast for northern England and Wales, while many other areas could also see the mercury plunge.
BBC weather forecaster Rob McElwee said the coldest weather would be in north-west England and England-Wales border areas, with temperatures dropping as low as minus 7C.
Belfast would see temperatures on New Year's Eve of minus 2C, London around zero, and Cardiff just below zero, he added.
There is unlikely to be any let up in the cold weather for the first days of 2009.
On New Year's Day cold temperatures and lots of fog are set to persist, with thickening fog over north-west England and the West Midlands.
A little sunshine may break through in western Scotland, Wales and southern England. Spots of rain and snow may fall in north-east England and eastern Scotland, with a possibility of black ice.
By 2 January more sunshine is expected, but the cold weather will remain for the foreseeable future.