Miley Cyrus and Liam Hemsworth sealed the new year with a kiss. And, if reports are to be believed, they might have even made their relationship official.

It has been reported that the couple secretly tied the knot at a family fancy dress New Year's Eve party at SeaWorld San Diego.

According to an NW insider, Miley and Liam got wed on the spur of the moment as their respective families gathered in San Diego for the holidays. Their family were reportedly only told of the hasty nuptials hours before the wedding took place.

The loved-up pair are believed to have written their own vows for the ceremony, in which they said they were each other's soulmates, according to Mail Online.

"It was all extremely last-minute," the source told the magazine. "Liam's entire family flew over for the holidays and the Cyrus family were in town too. It just seemed like a no-brainer to do it while everyone was together".

Family! #inlaws (no law)

A photo posted by Miley Cyrus (@mileycyrus) on

Miley posted several photos from the family gathering, including a photo captioned with the hash-tag 'in laws', featuring Liam's mum, Leonie Hemsworth, with Miley's mum, Tish Cyrus, and Elsa Pataky's mum Cristina Pataky Medianu.

Earlier, the 24-year-old singer shared a photo of her fiancé dressed in shiny gold trousers and a black shirt with his hand outstretched, as though asking her for a dance.

Miley captioned the photo: "Sorry. My dude is HOT."

But if they did indeed get married, there was no white wedding dress for Miley, who does things in her own uniquely sparkly style.

Sorry. My dude is HOT.

A photo posted by Miley Cyrus (@mileycyrus) on

The Wrecking Ball star wore a sequined skirt with a rainbow-coloured top and accessorised her outfit with rainbow stick-on diamontes.

And as the clock struck midnight the We Won't Stop singer shared a photo with fans on Instagram as the rumoured newlyweds shared a passionate kiss, with the photo garnering over half a million likes in the first hour.

The photo had everyone speculating that there might be more to the celebration, amid reports that the couple are eager to start a family soon and have been considering adoption.

It was previously reported that the celebrity couple were planning a summer beach wedding in Hemsworth's hometown in Australia.

Miley Cyrus and Liam Hemsworth
Miley and Hemsworth started dating after meeting on the sets of movie The Last Song in 2009 Getty