From the ancient Inca city of Machu Picchu in Peru and the Great Wall in China to Ramabai Ambedkar Maidan in Lucknow and colonnaded Connaught Place in Delhi, the sound of 'Om' reverberated through India and the world in celebration of the traditional fitness regime that combines spirituality and physicality.
Politicians, bureaucrats, students, judges and simply yoga enthusiasts gathered at offices, parks and even the road at specially held yoga camps to observe the day.
Dressed in a white T-shirt and trousers, Modi said yoga had now become part of every person's life.
"Many countries which do not know our language, tradition or culture are now connecting to India through yoga. The practice, which connects body, mind and soul, has played a big role in binding the world too," he said.
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In a series of tweets, Modi said later, "Today, Yoga has become a part of so many lives. Yoga's popularity outside India is high & has connected the world with India."
Prensha, 19, came to Lucknow from neighbouring Sitapur district and was thrilled to be doing asanas along with Modi.
"Modi coming here and performing yoga in the company of children and youths was perhaps the most surprising event of my life," she told PTI.
In Delhi, nearly 77,700 people braved pre-dawn showers and gathered at venues across the city.
AYUSH ministry officials estimated that the maximum gathering of 50,000 people was at the Red Fort lawns, followed by 10,000 yoga enthusiasts coming together in Connaught Place and about 9,000 at a DDA park in Rohini.
Though Modi was in Lucknow, his colleagues, Union ministers M Venkaiah Naidu and Vijay Goel, went to Connaught Place, With them were Delhi Lt Governor Anil Baijal and Delhi Chief Minister Arvind Kejriwal along with BJP's presidential candidate Ram Nath Kovind.
External Affairs Minister Sushma Swaraj joined a yoga session organised by her ministry with nearly 100 diplomats from various missions. Stressing that yoga belongs not merely to India, she said, "Excellencies, yoga is not merely about physical well-being through asanas or postures or pranayam or breath control. It is a science to attain inner peace, it is the art to attain equanimity."
While similar scenes were seen in other parts of the country, many gathered in places across the world, including iconic landmarks like the London Eye and Eiffel Tower, to celebrate the day.
At the UN headquarters in New York, people from all walks of life congregated at the North Lawns to participate in the 'Yoga Session with Yoga Masters'. The UN issued special stamps to commemorate the day. Delivering the secretary general's message, an official said yoga can make an important contribution in achieving a healthy life and promoting well- being at a time when the world is striving to achieve sustainable development goals.
The UN General Assembly had made a declaration in December 2014 that every June 21 would be observed as International Day of Yoga, a move that India lobbied hard for.
The focal point of the first International Day of Yoga celebration in 2015 was New Delhi's Rajpath. The event made it to the Guinness World Records with 35,985 participants performing asanas at one venue and 84 nationalities being part of it.
Last year, the main function was in Chandigarh.