Baywatch co-stars Zac Efron and Alexandra Daddario have denied rumours they are dating.

The High School Musical actor and San Andreas star sparked speculation they had embarked on a romance when Alexandra shared a photograph of Zac kissing her on the cheek backstage at the MTV Movie & TV Awards earlier this month (May17).

Since then, the rumoured couple have been paired together for Baywatch promotional duties and they were the only two cast members to head to Sydney, Australia for the film's Bondi Beach premiere this week (beg15May17).

However, Zac played down the romance rumours to Australia's Daily Telegraph by saying, "As far as I know, she hasn't said yes."

Alexandra added that she understands how the speculation has surfaced because of their onscreen love story in the reboot of the popular '90s TV show.

She said it "makes sense because we are love interests in the movie" before cheekily pointing to her co-star and saying,"But this is a lot for me to handle."

In the movie, Zac plays disgraced Olympic gold medal-winning swimmer-turned-lifeguard Matt Brody, while Alexandra plays his fellow new recruit, a surfer named Summer, and they both went to serious lengths to get their bodies into peak physical shape for the movie.

"It's all for the character, to achieve an aesthetic and a look. It's amazing how much you can put yourself through to achieve that transformation into the character," Zac said.

Zac, 29, is no stranger to dating co-stars. He was in a relationship with High School Musical actress Vanessa Hudgens between 2005 and 2010. He most recently dated model Sami Miro and they split in April 2016 after almost two years together.