Justin Bieber and his new girlfriend Sofia off on holiday for her 18th birthday

Justin Bieber and Sofia Richie - who celebrated her 18th birthday on Wednesday - have jetted off on holiday and shared flirty pictures on Snapchat.

The Cold Water hitmaker and model - who celebrated her 18th birthday on Wednesday - were spotted at Van Nuys Airport, Los Angeles, in matching grey and white tracksuits boarding a private jet and the blonde beauty shared flirty pictures of the couple on her Snapchat account.

Sofia - who previously revealed she was battling sickness on her big day - is seemingly back to full health as she enthusiastically captioned one picture: "Getaway!"

In a video, an excited Justin runs up and down the gangway of the plane and Sofia jokingly describes him as "Mental".

The couple confirmed their romance two weeks ago but the union was met with drama, as the pop sensation's ex-girlfriend Selena Gomez became embroiled in a public spat with the star.

The 24-year-old singer publicly scolded Justin when he threatened to make his Instagram page private after fans lashed out over pictures of his new love, and they accused each other of cheating during their on/off romance.

True to his word, Justin disappeared from the photo sharing site and Selena is now said to be stressed and needing time off work to rest.

A source revealed: "Justin and Selena's relationship is notoriously rocky and it hasn't been easy to see him move on so publicly with Sofia.

"But Selena is used to seeing him with other women - it's the combination of being over-worked and under pressure.

"She's been touring for four months non-stop and won't rest until mid-December with her 'Revival' tour still to hit Europe and South America.

"There's real concern and the plan is to talk to her in the next few days to ask her to consider taking some time off."

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