SYDNEY (AFP) - A dazzling display of fireworks lit up Sydney Harbour on Thursday as Australia's biggest city welcomed the New Year in spectacular style, defying terrorist fears days after a deadly siege.

Then in Hong Kong, brilliant bursts of colour over Victoria Harbour launched the party for millions across Asia.

From London to New York to Rio, millions around the world were set to celebrate as the clock ticked past midnight, ringing in 2015 with massive fireworks displays, concerts and light shows.

In Sydney, rocked by deadly drama just before Christmas when an Iranian-born gunman with a history of violence and extremism took 17 hostages in the city's financial hub, tonnes of fireworks exploded over the harbour watched by a crowd estimated at more than one million.

"We are celebrating that we are a multicultural, harmonious community but we will be thinking about what happened," Lord Mayor Clover Moore said in reference to the incident in which two hostages and the gunman died.

In the aftermath of the siege, Prime Minister Tony Abbott said security agencies had picked up a heightened level of "terrorist chatter" and warned that "the terror threat remains high and... at this level, an attack is likely".

But the fireworks display went ahead without incident. Brilliant bursts of colour lit up the harbour in spectacular fashion in the midnight showpiece, with fireworks cascading off the Harbour Bridge, shooting off the Opera House and streaming across the sky in one of the world's first major celebrations to ring in 2015.

In Hong Kong, hundreds of thousands of people crowded the city's promenades to watch the eight-minute pyrotechnic display after a year which had seen busy thoroughfares paralysed by pro-democracy protests in the final months of 2014.

"I think a more peaceful year would be good for everybody," said Louis Ho, 65. Students on one promenade handed out free hugs.

REMEMBRANCE FOR LOST AIRASIA FLIGHT

In China, Beijing's bid to stage the 2022 Winter Olympics was the theme of celebrations. Concert pianist Lang Lang was the star performer at an extravaganza at Olympic Park.

The Chinese capital has held New Year countdowns at the historic Temple of Heaven since 2011, but moved the event to the site of the 2008 summer games to raise the profile of its winter Olympics bid.

In Taiwan, the landmark skyscraper Taipei 101 was at the centre of celebrations, with performances by pop singers and a firework display at midnight expected to attract hundreds of thousands.

And in Japan, the Meiji Jingu shrine in Tokyo brought out stocks of lucky charms and set up large offertory boxes as it prepared to welcome a huge wave of worshippers overnight. The huge shrine expects three million visitors in the first three days of the new year.

Hundreds of revellers were due to gather around a popular British-colonial era shopping arcade in central Delhi to greet the New Year, braving unusually chilly weather. Pubs and eateries were festooned with fairy lights and brightly coloured balloons.

But in Malaysia, a sombre mood prevailed after the crash of AirAsia Flight QZ8501 carrying 162 people in Indonesia and flooding in the country's north-east which has displaced almost 250,000 people.

Year-end countdown celebrations have been cancelled, with many companies instead launching fund-raising campaigns for flood victims.

In Indonesia, Surabaya was holding a candlelight vigil in the hours leading up till midnight to remember the people on the plane which departed that city on Sunday.

In Afghanistan, the last French troops in the country held a ceremony in Kabul to mark the end of their deployment after Nato combat operations closed down as a new "train and support" mission takes over.

HASSELHOFF IN BERLIN

The end of another era will be remembered in Berlin with Baywatch star David Hasselhoff joining a huge open air concert in front of the Brandenburg Gate, where he famously sang for freedom after the Berlin Wall fell 25 years ago.

Dubai has promised to dazzle again with a pyrotechnic and lights show at Burj Khalifa, the world's tallest tower.

In Paris, the Champs-Elysees will be reserved for pedestrians to let them watch a visual spectacle projected onto the Arc de Triomphe 15 minutes before the start of the new year.

The ticking of the clock past midnight will be significant for Lithuania as it adopts the euro. Another Baltic state, Latvia, takes over the rotating presidency of the European Union, putting it on the front line of negotiations with neighbouring Russia over the crisis in Ukraine.

In Spain, millions of revellers will descend on Madrid's Puerta del Sol while in Barcelona a massive fireworks display will be held.

London stages New Year's Eve fireworks along the Thames and Edinburgh will be holding its traditional Hogmanay street party.

Marking 2015 on Copacabana beach in Rio de Janeiro, more than two million people are expected to attend a huge fireworks show that will open celebrations marking 450 years since the founding of the city.

And in New York about one million revellers are expected to descend on Times Square to watch the New Year's Eve Ball Drop.