Pharrell Williams' hit track 'Happy' is set to be played for almost two weeks straight on an online streaming service.

iHeartRadio is honouring the United Nation Foundation's International Day of Happiness on Wednesday (March 20) by playing Williams' song for 13 days.

The music started on Tuesday (March 18) on a dedicated online channel and it will end on March 31.

Williams is this year's celebrity ambassador of the United Nation Foundation's International Day of Happiness.

The song meanwhile features on the singer's new album 'G I R L'.

Watch the video for 'Happy' below: