New Year's celebrations across the world have ushered in 2017 with dazzling fireworks displays and crowded streets amid tightened security measures for the festivities.

There was a huge police presence on the streets of London as spectators from nearly 100 countries flocked to the Thames to watch the night sky light up as Big Ben struck midnight.

With memories of the lethal Berlin lorry truck attack still fresh, London mayor Sadiq Khan assured crowds the capital was "as safe as it possibly can be".

After the event passed successfully, he haled it as demonstrating to the world that London "is open to all".

Newcastle welcomed the New Year with a spectacular display of fireworks, but the festivities proved too much for some revellers who obviously had a touch too much to drink.

Generally, however, the crowds were well behaved, mindful of the fact they were being guarded by armed police.

In Scotland, Hogmanay celebrations were expected to attract a crowd of up to 80,000 people to Edinburgh for the sold-out, world-famous event, described as the UK's largest outdoor winter festival.

Cities in the Pacific island nations of Samoa, Tonga and Kiribati were among the first to bid farewell to 2016, before fireworks were launched from the top of Auckland's Sky Tower.

Two pyrotechnic shows followed at Sydney Harbour and doused Australia's iconic bridge in the bright light of an estimated seven tonnes of fireworks.

The city's display also saw Sydney Harbour Bridge turned purple in a tribute to Prince, while David Bowie was honoured with space-themed visuals in a nod to the late star's hit, Space Oddity.

Meanwhile, red starbursts exploded above the Kremlin for the Russian occasion, which marks the country's major gift-giving holiday.

In Europe, fireworks in Helsinki also signified the beginning of the centenary year of Finnish independence.

Mr Khan said the "dazzling display" was "celebrated safely and in style" thanks to the work of the emergency services.

"People came from all over the world to kick off the New Year in our great city and our world-renowned fireworks display was broadcast around the globe, delivering the message, once more, that London is open to all," he added.

Lucas Agostinis de Paula, 22, an engineering student from Brazil, said the event was "amazing", adding: "I've never seen anything like this in my life."

Asked if he had been worried about coming to London for New Year's Eve, he said: "Yes, because there is too many people together."

But he added: "I felt safe tonight because they were looking through the bags."

Around 3,000 officers were on duty within and outside ticketed areas, while armed police were also set to be a fixture on the capital's Tube trains as they travel between jobs in a move aimed at reassuring passengers.

Scotland Yard said officers made 33 arrests for crimes including 10 assaults, two sexual offences and a drugs offence.

Fears of a mass-casualty terror plot targeting one of the country's New Year events heightened after lorries were used in devastating attacks on crowded areas in Nice and the German capital.

British Transport Police (BTP) said it would also be extending officers' working hours on the night for a second year running.

BTP Superintendent Andy Morgan said: "We developed and improved our security plan for last year's New Year's Eve event following the atrocities in Paris in the previous November and we, of course, have looked at good security, a thorough security boost following a different type of threat in Nice back in July."

Some anticipated the arrival of the New Year on boats that darted back and forth in front of the London Eye, which projected rainbow spotlights from its base, while crowds lining the Victoria embankment held their phones aloft with the torches on to illuminate the shoreline.

The site's DJ acknowledged international visitors and said they were welcome to the capital to kick off 2017, with music keeping them entertained in the hours leading up midnight.

As the UK marks the start of 2017, other regions of the world will still be waiting for the much-anticipated stroke of midnight.

The New Year arrived in New York at 5am London time on Sunday, while places such as Baker and Howland islands in the Pacific will be the last to ring it in at about midday GMT.