Latest: Fireworks light up Tokyo and Sydney skies as world welcomes 2018

LATEST: Sydney is welcoming 2018 with rainbow-themed fireworks to celebrate new same-sex marriage rights.

Australia, Japan and China are among the countries who have already welcomed in 2018 - all with spectacular fireworks displays.

Security will be tight ahead of similar events across Ireland and the UK tonight - including at Edinburgh's Hogmanay celebrations, for which chief superintendent Kenny MacDonald said security had been completely reviewed.