Las Vegas rocks on day one of the iHeartRadio festival

Day one of the iHeartRadio festival got off to a flying start on Friday with a huge host of rock and pop stars turning out.

The crowds in Las Vegas were treated to the likes of Usher, Rihanna, Bon Joni, Green Day, Pink, Gwen Stefani and Lil Wayne.

Held at the MGM Grand over two days, this is the second time the annual event, which is aired through the iHeartRadio digital music platform, has taken place.

Radio and TV presenter, Ryan Seacrest, who is the festival's host, was joined by a guest appearance from Britney Spears. Ryan has previously praised the event, saying that the sheer size and standard of the lineup sets it apart from other festivals. He added that that the spark for the most unexpected collaborations can happen at events like this one.