Justin Bieber makes surprise appearance on Knock Knock Live ahead of ‘big announcement’ this week

Canadian pop star Justin Bieber has sent Twitter into a meltdown ahead of his appearance on Ryan Seacrest’s new show Knock Knock Live.

Broadcaster FOX released teaser clips from the 21-year-old’s episode ahead of the show’s premiere tonight.

Wearing a black cap, jeans and a baggy t-shirt the Baby singer can be seen knocking on the door of a church in Lynwood, California much to the surprise of the family inside.

Bieber visited a man and his child Noah – who has Down’s Syndrome – to show them some love and “bless” the young boy. Viewers will have to tune in to the show to find out Bieber’s big surprise for the pair.

A second clip was also released showing the singer arrive at one girl’s house before leading her hand in hand to her Quinceañera - the celebration of a girl's 15th birthday.

Clearly excited ahead of the show one Belieber tweeted: “The videos of Justin on knock knock live made me shed tears he's so sweet omfg #MtvHottest Justin Bieber.”

Another posted: “WHY COULDN'T THIS HAPPEN TO ME ON MY QUINCEANERA @justinbieber come to my house #KnockKnockLive.”

Bieber is the latest star to appear on the show after David Beckham who knocked on the door of the unsuspecting Gonzales family and presented them with iPhones and a cheque for $100,000.

The clips come a day after Bieber excited his fans by teasing news of a big announcement.

His manager Scooter Braun tweeted, “Hey @justinbieber I'm fired up!! Lol” to which the singer replied: “yep. Big announcement this week.”

Fans have speculated that the music star may announce his next album or single.