One Direction star Niall Horan.Wallko

The One Direction hunk, 21, has sent jealous fans into a meltdown on Twitter after he was spotted cuddling up to a pretty brunette named Melissa Anne, also 21, over the weekend in Melbourne.

One heartbroken fan, Vanessa, tweeted: "OMG Niall Horan and Melissa. They were seen in a casino, they kissed. And he held her by the waist and playing with her hair (sic)."

While Iena, wrote: "melissa was a fan and now here she is making out and hooking up with niall horan how did she do it (sic)."

And another fan, who goes by the user BibiHoran, added: "The moment when i heard about @NiallOfficial and melissa i was shocked, happy for him and really sad at the same time #mixedfeelings (sic)."

However, some people have been saying the stunning woman already has a boyfriend and she and Niall are merely friends.

The Irish singer has been enjoying his time Down Under since landing in Australia almost two weeks ago with his band mates Harry Styles, Liam Payne, Louis Tomlinson and Zayn Malik for their On The Road Again tour.

The boys have been spotted exploring zoos, tucking into delicious food at local restaurants and posing with fans during nights out.

They've already played six dates across Sydney, Adelaide, Brisbane and Melbourne, and will finish up the Australian leg of the tour on Friday (20.02.15) in Perth before jetting to Asia.