Mariah Carey is ''cautious'' around James Packer.

The 'Without You' hitmaker is reportedly romancing the Australian billionaire but isn't quite ready to ''let him in yet''.

A source told E! News: ''They are not talking marriage. That's ridiculous.

''She's enjoying his company, but she's also trying to remain cautious. This trip is a chance for her to really get to know him. She hasn't 100 percent let him in yet.''

Meanwhile, the 47-year-old businessman has reportedly been courting Mariah - who has four-year-old twins Monroe and Moroccan with estranged husband Nick Cannon - for a number of months.

The 45-year-old star is believed to have been treated to a number of lavish presents including a room full of flowers for her hotel suite as well as travelling to Las Vegas to support her ahead of her Mariah #1 to Infinity residency.

Meanwhile, Mariah's ex Nick previously suggested there's a possibility of the couple reuniting.

He said: ''It's one of those things, I'm a hopeless romantic too. Through this learning process, you never say never.

''To me one thing I know, that will always be the love of my life, always be my family and that's never going to change.''