The world has begun welcoming 2015 with a series of spectacular displays already taking place around the globe.

Sydney had a tropical-style theme featuring shimmering gold and silver palm tree pyrotechnic effects.

More than 1.5 million revellers crowded along the shores of the Australian city's harbour to watch seven tons of fireworks explode over the Harbour Bridge, Opera House and other locations.

The festivities came just two weeks after Iranian-born self-styled cleric Man Haron Monis took 18 people hostage in a cafe siege which ended with the deaths of him and two detainees.

A tribute to the killed hostages was displayed on the pylons of the bridge during the main display, and an extra 3,000 police officers were patrolling the city.

In Auckland, New Zealand, a giant clock on the city's landmark Sky Tower counting down the minutes until the New Year.

There was then a huge fireworks display from the top of the building at midnight.

Hong Kong also saw in 2015 in spectacular fashion, with the traditional pyrotechnics show over Victoria Harbour.

The waterfront was crowded with spectators who watched the eight minute firework display above the iconic Hong Kong Convention and Exhibition Centre.

Residents of North Korea's capital Pyongyang were treated to a lavish display of fireworks at midnight.

The country had its first grand New Year's Eve celebration in the city three years ago, after Kim Jong-Un came to power following his father's death.

And since then, it has become an annual event.