Katy Perry made children cry after gatecrashing a five year old's birthday party.

The 'Dark Horse' hitmaker dressed up as a clown for the video for her track 'Birthday' and carried out a prank at a party, where she attacked a man with a piñata stick and staged a car accident, but the spoof incident left children in tears.

Eye witnesses told TMZ, Katy pranked a real birthday party and most of the guests had no idea it was a joke.

Children were crying and one woman ''stormed away'' visibly upset by her antics.

The hidden camera gag was shot at Knollwood Country Club outside Los Angeles and a video obtained by the website shows one little girl saying, ''Mommy, I want to leave.''

During an interview on 'Jimmy Kimmel Live', Katy spoke about going ''undercover'' at the bash, but didn't mention the fall out.

Speaking earlier this week, she said: ''I just did a music video completely undercover as five of the world's worst birthday entertainers, because I was sick of making gorgeous music videos where I'm sexual.''

Jimmy joked: ''People are sick of that, yeah, really tired of looking at you.''

Katy, 29, then previewed a clip of the video which sees her dressed as a clown drinking and burping, saying: ''I'm not really a birthday party entertainer, I'm just trying to get some cash on the side,'' adding, ''Happy birthday kids.''