New Year's Eve: World welcomes 2017 with huge celebrations after traumatic year

Many countries have launched their biggest ever firework displays

Millions of people across the world took to the streets to celebrate the start of the new year, in a blaze of fireworks.

But the mood was tinged with sadness after the traumatic and tumultuous time seen in 2016.

Berlin launched a huge firework display from near the Brandenberg Gate, for instance – but it was marked by the memory of the attack on a Christmas market in recent days.

Security was stepped up across Europe and Britain. Officials including London mayor Sadiq Khan said they were confident that the right mix of safety and enjoyment had been achieved.

Celebrations in Istanbul were marred by mass shooting at a nightclub which killed at least 39 people. The gunman was still at large.

In Russia – which in one sense celebrates the New Year a number of times because of its various timezones – 2017 was welcomed with a stunning firework and light show.

But it also came with a warning from Putin that 2016 had been a "difficult year" and that people should work harder to make 2017 a better one.

Meanwhile, New York saw problems of a different kind when singer Mariah Carey's performance in Times Square was beset by technical difficulties.

People leave a nightclub in Istanbul after it was attacked on 1 January (AP)

Tonga and Samoa were among the first places in the world to welcome the new year.

Sydney in Australia celebrated by unleashing its biggest fireworks display in history.

More than a million crowded around its famed harbour and opera house to watch firecrackers and flaming starbursts fill the night's sky.

The show paid homage to Prince and David Bowie and was set to a musical medley inspired by the late singers.

The seven tons of fireworks launched from barges on the harbour also included a “Willy Wonka moment” in tribute to the late actor Gene Wilder's most famous role,.

Japan celebrated at 3pm GMT, with temple bells sounding at midnight as families flocked to shrines for the country's biggest holiday.

Beijing and Shanghai, China's two largest cities, passed New Year's Eve at 4pm GMT in a state of security lockdown, according to Chinese media reports citing police.

Two years ago, more than 30 people died in a deadly stampede on Shanghai's waterfront, where 300,000 people had gathered to watch a planned light show.

This year, a "leap second" is being added to the end of the year to compensate for a slight slowing of the Earth's rotation. 2016 is already a leap year.