Australia's largest city Sydney will welcome 2018 with a rainbow-themed fireworks spectacular hailing the introduction of same-sex marriage, amid strict security for the nation’s festivities that will launch celebrations worldwide.

More than 1.5 million spectators were packing the city’s foreshore to watch tonnes of pyrotechnics light up the night sky in the first major New Year’s bash.

The technicolour display will include a rainbow waterfall of fireworks cascading off the Sydney Harbour Bridge to mark Australia’s legalisation of same-sex marriage following a nationwide postal vote in support of change.

“This is a fabulous way to see out 2017 — the year that four out of five Sydneysiders said a resounding ‘Yes’ to marriage equality,” said Sydney Lord Mayor Clover Moore.

Hollywood heart-throb Hugh Jackman will add star power with a 20-second gold-and-silver pyrotechnics set, fulfilling a lifelong dream of designing a firework for his home town.

  Celebrations then moved to Asia, the Middle East, Africa, Europe and finally the Americas, with dazzling light shows bidding farewell to 2017.