The New Year - and fresh decade - was welcomed in across the world with fireworks and music galas, but Australia's celebrations were overshadowed by deadly wildfires while protests dampened the festive mood in Hong Kong and India.

New Zealanders were among the first to welcome 2020 on Wednesday, with fireworks lighting up the sky over the capital, Auckland.

Large crowds thronged Sydney harbour to watch Australia's famous New Year's Eve fireworks, even as smoke from wildfires turned the evening sky in nearby towns blood red.

Many towns along the country's eastern coast cancelled their fireworks as thousands of people swarmed to beaches to escape the fires.

Hong Kong's government also cancelled its popular New Year's Eve fireworks in Victoria Harbour due to security concerns as protesters staged more rallies against what they see as an erosion of democracy in the semi-autonomous Chinese territory.

People in India also welcomed the New Year with protests, angered by a citizenship law they say will discriminate against Muslims and chip away at the country's secular constitution.