She certainly isn't shy about flaunting PDA with her boyfriend, Tyga.

Kylie Jenner has posted racy topless photos of the couple to mark the rapper's 27th birthday, calling him "irreplaceable".

In the sexy shoot, Jenner, 19, is wearing a pair of blue denim jeans and nude high heels, and no top, while she strategically covers her bare chest with her arms.

Tyga - who is also shirtless - shows off his ample tattoos with his arms around Jenner.

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Jenner captioned the image: "Happy birthday baby".

It comes days after the Keeping Up With the Kardashians star and make-up entrepreneur posted a series of provocative photos on Instagram, wearing sheer lingerie and teasing her own line of bras and knickers.

Jenner and Tyga have been dating on and off since Jenner was 17.

"The first year we started hanging out, everyone around him told him not to be with me," Jenner said in an interview with Complex this year, Us Weekly reports.

"I still get comments like, 'don't be with him'. But we're not doing it for the public - we love each other.

"We need to be together at all times. We never get mad at each other, we just figure things out."

Of course, their relationship became even more complicated this year when Jenner's brother, Rob Kardashian, started dating Tyga's ex, Blac Chyna (the former couple share a son, King Cairo).

Rob and Chyna welcomed a baby girl, Dream Kardashian, this month.

Tyga and Kylie Jenner attend the Alexander Wang Spring 2016 fashion show during New York Fashion Week. Photo / Getty
Tyga and Kylie Jenner attend the Alexander Wang Spring 2016 fashion show during New York Fashion Week. Photo / Getty