James Corden, Pharrell and Sia all get behind new iPhone 7

Sia, James Corden and Pharrell all pitched in to help launch the new iPhone. Photos / AP, supplied

Apple's new iPhone is the talk of the town today, especially after the tech giant rolled out a couple of massive celebrity appearances to promote it.

First, Apple's CEO Tim Cook followed in the footsteps of Justin Bieber, Elton John, Mariah Carey and Michelle Obama and scored himself a spot on Carpool Karaoke.

In a shorter-than usual clip with James Corden, Cook sang his heart out to One Republic, messed around with Siri, did some outfit-planning and belted out Sweet Home Alabama with none other than Pharrell.

Apple also managed to get one of the biggest pop stars in the world, Sia, to perform at the launch. But it wasn't any old performance; it was her first live performance of her latest single The Greatest.

The hit, featuring rap super star Kendrick Lamar, was only just released this week. But Sia belted it out for Apple, along with a performance of her hit Chandelier, while her video dancer Maddie Ziegler performed alongside her.