SYDNEY - Revellers across the globe began ringing in the New Year but a Bali terror warning and a deadly shooting in Finland stoked security jitters, already high after a failed US bomb plot.

Police were on alert in many world cities after the thwarted Christmas Day attack on a US-bound plane, as party-goers from Vanuatu to Vancouver began raising glasses to 2010 and closing the door on a decade scarred by wars, terror attacks, natural disasters and financial turmoil.

The party spirit was alive and well in Sydney, where a vast display of fireworks burst into the night sky at midnight.

The US embassy in Indonesia said it had received a warning of a possible attack on the resort island of Bali, the scene of multiple bombings targeting Westerners, but local authorities denied any knowledge of such an alert.

In Helsinki, five people were killed after a lone gunman opened fire at a shopping centre, the third major shooting in Finland in the past two years. A sixth body found was thought to be that of the killer.

For international troops in Afghanistan, it was business as usual, with soldiers maintaining their normal schedule of operations, after two deadly Taliban attacks claimed the lives of eight Americans and five Canadians.

In Australia, an estimated 1.5 million people crowded the harbour foreshore for the high-tech fireworks display on the iconic Sydney Harbour Bridge.

Paris's Eiffel Tower was to be transformed into a multicoloured light show while in Berlin, more than one million revellers were expected on the boulevard leading to the Brandenburg Gate, the symbol of German unity.

Celebrations in Britain centre on the London Eye, the giant wheel across the river Thames from the Houses of Parliament and Big Ben, the world's most famous clock.

A downpour of confetti was to mark midnight at New York's traditional mass celebration in Times Square in the heart of Manhattan,

Amid security jitters rekindled by the bomb plot against a Detroit-bound passenger jet claimed by Al-Qaeda, undercover police, surveillance cameras, uniformed teams and radiation and biological detection equipment were to monitor the crowds.

"It will be a full fledged deployment of resources," city police Commissioner Raymond Kelly said. "We assume here that New York is the number one terrorist target in America."

In Sydney, as people gathered for celebrations, police minister Michael Daley urged revellers to keep a lid on their drinking.

"If you're one of these fools that can't handle their grog and likes to go out and ruin other people's nights, make yourself a new year's resolution to grow up and behave yourself and start practising that on New Year's Eve," he said.

Around half a million revellers were expected to crowd Hong Kong's harbour front to watch 9,000 fireworks.

But in Thailand, police banned fireworks after a New Year's Eve blaze at a Bangkok nightclub a year ago killed 65 revellers.

In China, President Hu Jintao praised the past year of 60th anniversary celebrations for the People's Republic in a televised address, saying: "the people of China became further determined to continue the advance of socialism with Chinese characteristics."

Security was tight in Afghanistan and Pakistan after a year of bloodshed for both countries, which are fighting growing insurgencies from Al-Qaeda and Taliban-linked militants.

In Pakistan, hardliners who consider New Year festivities anti-Islamic have in the past gate-crashed luxury hotels and broken up parties.

In Karachi, the young usually welcome in the New Year with gunfire and crackers, but a deadly suicide attack during a holy Shiite Muslim ceremony this week has dampened enthusiasm.

"It is hard to celebrate when our city and country is passing through such deep trouble," said Zohaib Memon, 23, a business management graduate.

In Indian Kashmir, locals were set to enjoy some of the first major New Year celebrations since an insurgency broke out 20 years ago, despite protests from Islamic hardliners who object to the "anti-Islamic" partying.

In the Philippines, shaken by natural disasters in recent months, nearly 50,000 villagers were likely to spend the first few months of 2010 in evacuation centres amid concerns the Mayon volcano could erupt at any time.

The mood was sombre in the Pacific archipelago of Tonga, where midnight masses were held at the close of a tragic year in which a ferry sinking in August and a lethal tsunami a month later killed more than 80 people and destroyed the livelihoods of thousands.