Bieber's ice bucket challenge

Justin Bieber is daring his fans to take the so-called 'ice bucket challenge'.

The 20-year-old pop star is the latest in a long line of celebrities to join in the shiver-inducing viral video campaign to raise funds and awareness for neurodegenerative disease ALS.

Justin posted two videos online Sunday showing himself tossing a bucket of ice-cold water over his head before challenging his fans around the world to do the same.

'Alright, second ice bucket challenge today,' he says in the clip. 'I nominate my Beliebers all over the world. I know you guys got an ice bucket somewhere,' Justin dares before splashing the frigid H2O over his head.

'Accept? U have 24 hours #beliebers or u can donate to ALS here. #alsicebucketchallenge #giveback :) (sic),' the singer then wrote on his social media pages, including a link to the official ALS website.

The video followed another in which Justin nominated friend Ellen DeGeneres and US President Barack Obama.

'I accept, now I nominate @Theellenshow my main man President Barack Obama and @Chrisdelia #alsicebucketchallenge,' he captioned another Instagram video of himself trying to catch his breath after throwing the water over his head.

It didn't take long for Justin's fans to follow suit.

The pop star, who was challenged by manager Scooter Braun to take the plunge, had re-tweeted several fan videos within minutes of posting his own.