Rescue and relief work was carried out through the night, an official in the office of Varanasi District Magistrate told Xinhua, adding that at least 30 people have been injured, half of them seriously.
Varanasi is the parliamentary constituency of Prime Minister Narendra Modi and is a famous religious and tourist city.
The incident occurred when two huge beams of the under-construction flyover came crashing down, trapping dozens of vehicles under them. The National Disaster Response Force teams used gas-cutters to bring out dead bodies from under the debris and those injured from inside the vehicles.
According to eye-witnesses, the area where the incident occurred is often crowded and traffic moves at a very slow speed.
Expressing grief over the incident, Prime Minister Modi tweeted: "Extremely saddened by the loss of lives due to the collapse of an under-construction flyover in Varanasi. I pray that the injured recover soon. Spoke to officials and asked them to ensure all possible support to those affected."
Meanwhile, state Chief Minister Yogi Adityanath reached Varanasi late in the night and met those injured. He also ordered an inquiry into the incident.
Adityanath's office has also announced a compensation of 7,322 U.S. dollars to each family that lost member in the accident, while 2,928 U.S. dollars would be given to each of injured in the tragedy.
The state-run broadcaster All India Radio said Adityanath has set up a three-member committee to probe the flyover collapse and asked it to submit its report within 48 hours.
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