The British comedian, who has just taken over the hosting gig on The Late Late Show, was introducing Couric to his audience when she appeared to slip and fall.

The resulting tumble sent her onto the studio floor where she lay motionless.

The studio band fell silent, the audience's applause dissolved into stunned silence and a horrified Corden sprinted across the studio to assist Couric.

But the fallen figure was a stuntwoman – take a bow, Heidi – and the real Couric then revealed herself at the top of the stairs declared what was now apparent to everyone: it was an April Fool's Day prank.

"Oh my God," Corden exclaimed, as he collapsed himself to the floor in shock. "That's ridiculous."

"Are you OK?" Couric asked him.

"I can't breathe," he said. "That's our worst nightmare. That is so funny. That is an amazing prank. We have been talking about these stairs, going back and forth, I was like, oh my God, Katie Couric has just died."

The stunt made a perfectly packaged viral clip, though it is clear that was the intention from the outset.

 

Since taking over the late (late) night hosting gig from Craig Ferguson, Corden has upped the ante in the chase for online audiences tuning into US talk show clips.

Jimmy Fallon, who has taken over hosting duties on the iconic Tonight Show, is the leader of the pack but his rivals, including Jimmy Kimmel and now James Corden, are pushing hard.

All three programs now produce viral clips daily, hoping to surf them into the online news cycle.

Corden's recent efforts include Carpool Karaoke, which featured Mariah Carey, and Every Tom Hanks Movie in 7 Minutes, which featured Hanks, in which the pair-recreated scenes from his entire film career.

 

In another, he and British footballer David Beckham pose in their underwear promoting a supposed "new underwear line."

 

Follow Entertainment on Twitter