It's time to go "from climate change to climate action" in efforts to save the planet, US pop star Pharrell Williams said at the United Nations on Friday.

Singer-producer Williams, 41, partnered with the United Nations Foundation on yesterday's International Day of Happiness to raise awareness and call for more action on climate change.

"If you look at our behaviour it's hard to believe we're all aware we only have one planet," Williams said in a General Assembly hall crowded with young people. "My main inspiration for being here today is that we're in trouble, but we can change that. This earth is our home."

The star is the creative director of the Live Earth movement, which campaigns for a climate deal to be reached before a global summit takes place in Paris in December.

At January's World Economic Forum in Davos, Switzerland, Williams and former US vice-president Al Gore announced that a Live Earth music event to demand action on climate change will take place across seven continents, including Antarctica, on June 18.

As part of the celebrations of International Day of Happiness, the UN Foundation and Williams launched the "Happy Party for a Happy Planet" campaign and created a website(globalhappyparty.com) with the support of Google where people can upload photos of themselves which will then be assembled in an animated image set to Williams' hit song "Happy".

"Music brought me happiness... You should know happiness is your birthright," Williams told the young audience.

"On this day we are using the universal language of music to show solidarity with the millions of people around the world suffering from poverty, human rights abuses, humanitarian crises and the effects of environmental degradation and climate change," United Nations Secretary General Ban Ki-moon said in a video message.

As the event wrapped up, the audience got up and started dancing to "Happy".

Williams later greeted young fans who swarmed the General Assembly hall's stage, sending UN security momentarily into panic as it struggled to contain the wave of screaming young people and their parents.

Earlier this week, Charlize Theron, Michael Douglas, James Blunt, Ed Sheeran and John Legend, among other celebrities, joined the United Nations #HappySoundsLike campaign to create "the world's happiest playlist."

The International Day of Happiness was established in 2012 by the United Nations General Assembly to recognise the importance of happiness and well-being as "universal goals and aspirations in the lives of people around the world."