The Delhi Police had received intelligence inputs about some terror outfits planning a "London-style attack" during the International Yoga Day celebrations at Connaught Place here.
In view of the alert warning of the attack similar to the one in London recently in which a man had ploughed a van into people, the police had barricaded with buses the entry points of roads leading to Connaught Place, sources said.
The police had only left some space for pedestrians to pass through, the sources said.
This had been done to ensure that even if a vehicle tried to enter the area, it would end up ramming into these empty buses, they added.
A three-tier security layer was thrown around the area to enhance the vigil, a senior police officer said, adding, that snipers were also stationed on certain buildings to keep a hawk eye vigil.
Police had received a specific input about a London-style attack being planned to disrupt the event that was being attended by various dignitaries, including NDA's presidential candidate Ram Nath Kovind, Union Minister M Venkaiah Naidu and Delhi Chief Minister Arvind Kejriwal.
As many as 10,000 people joined the dignitaries early this morning at the famed British-era market in the common Yoga performance.
A man had recently ploughed a van into Muslims leaving prayers at a mosque injuring 11 people near Finsbury Park mosque, north London.
In April, a hijacked beer truck rammed into pedestrians at a central Stockholm department store, killing four people, wounding 15 others and sending screaming shoppers fleeing in panic.