In pictures: Sydney extravaganza kicks off New Year celebrations worldwide
Hong Kong saw 2018 in spectacular style as the southern Chinese city staged a stunning fireworks display over its famous Victoria Harbour. Thousands thronged the harbourside to see the show illuminate the famous skyline as revellers danced to Auld Lang Syne.
In the Indonesian capital Jakarta, hundreds of couples attended a free mass wedding provided free by the authorities.
Three hours earlier Australia rang in the New Year with a spectacular display of rainbow-coloured fireworks cascading from Sydney Harbour Bridge, as partygoers marked the nation's legalisation of gay marriage amid tight security. Thousands turned out earlier in New Zealand's largest city Auckland for the annual New Year's Eve street party, marked by a major fireworks display from the Sky Tower.
Celebrations then moved to Asia, the Middle East, Africa, Europe and finally the Americas, with dazzling light shows bidding farewell to 2017. Stricter security has been a key focus amid fears that crowds could be targets for vehicle and other terror attacks.