American Idol host Ryan Seacrest has been caught making a series of bizarre comments to pop star and judge Katy Perry, apparently unaware he was live on television.

The awkward moment took place during the most recent episode of the singing contest as the show returned from a break.

Seacrest was pictured next to the judges' table but seemingly did not notice they were back on air.

"We're on," Perry whispered, but Seacrest either ignored her or did not notice.

"Your mum's pretty," he told her.

"My mum?!" a surprised Perry asked. Then she smiled and winked at the camera - possibly to make Seacrest realise they were live - and added: "Well, I hope the apple doesn't fall from the tree."

"You are too, but you're not a mum yet," Seacrest continued.

"Not yet," Perry replied.

"Wanna talk about it?" he asked.

"Don't start," fellow judge Lionel Richie warned Seacrest.

Eventually everyone worked out they were back on air, but the exchange left many viewers feeling uncomfortable.