Here are the latest developments:
Marco Frigatti, Senior Vice President of Guinness World Record, who made the announcement, said it was "an astounding achievement (and a) very rare one".
Addressing the delegates on the occasion in New York, External Affairs Minister Sushma Swaraj said it was "an idea whose time has come". Thanking the 192 UN member states who made International Yoga Day possible, she said, "The word 'yoga' means to unite, to join... we hope this will help bring the world together."
A video address by Prime Minister Narendra Modi was shown on the occasion. "This is a heritage of the world and humanity... A big dream starts with a small exercise of yoga," the Prime Minister said.
"The International Yoga Day is a wonderful addition to the UN calendar. I commend Narendra Modi and the government of India for taking this initiative," said UN Secretary General Ban ki-Moon.
Ms Swaraj also attended the celebrations were held at New York's Times Square, with hundreds of people joining a yoga session. A mass yoga session was held at the Visitor's Plaza in the UN Headquarters too -- a "first in UN history," tweeted MEA spokesperson Vikas Swarup.
This morning, PM Modi surprised everyone by joining a mass yoga session at Rajpath. "Who would have thought that Rajpath would become Yoga Path?" he said.
Giant digital screens beamed the event live from Rajpath, where security arrangements rivaled Republic Day celebrations.
Similar yoga events took place simultaneously across India in parks, churches, homes, on military ships, an army base in the desert and even mid-air on some flights.
Delhi Chief Minister Arvind Kejriwal, a critic of PM Modi, was also spotted at Rajpath performing yoga. "Yoga is a good thing. Everyone should do it," he told reporters.
The UN had announced June 21 as the International Day of Yoga last year after PM Modi's appeal at the General Assembly. The day was observed across the world - including Britain, where mats were rolled out along the banks of the River Thames and in Paris, under the Eiffel Tower.