Thousands of people laid out their mats and stretched into yoga exercises in New York's Times Square Sunday, including the Secretary General of the United Nations, to celebrate the first International Day of Yoga.

UN chief Ban Ki-moon, dressed in white, joined the yoga gathering late in the morning in one of the most recognizable squares in the world.

Ban hailed the many benefits the ancient exercise could bring to people around the world.

"To all of you I say: Namaste!" the UN leader told the crowd.

"My hope is that yoga will give people everywhere the sense and the oneness we need to work together to live in harmony and usher in a life of dignity for all."

The UN declared in December that June 21 would be a world yoga day, highlighting its health "benefits" for the public. That coincided Sunday with the annual session in Times Square for yoga on the first day of summer.

Hundreds of yoga mats were distributed free Sunday in New York, and pedestrian areas, typically hectic, were completely covered with peaceful people taking instruction from teachers by loudspeaker.

Yoga classes started at early in the morning and are scheduled to last until the evening.

Organizers said people in 187 other countries would also take part in yoga sessions Sunday.

Outdoor yoga classes were planned Sunday in major cities across the US and tens of thousands of people took part in New Delhi.

The world day was also championed by Prime Minister Narendra Modi of India, the birthplace of yoga.