The collapse of a flyover under construction in a busy commercial area in the eastern city of Kolkata has killed at least 20 people, injured more than 75 and buried up to 150, in a disaster the Indian media was quick to label "man-made".
Video aired on Indian television showed a massive concrete column and 100m stretch of the 2km flyover crumpling in a plume of dust yesterday, crushing auto rickshaws and people during the busy lunch hour when crowds were flocking to the hawker stalls under the flyover.
One eyewitness told reporters that he heard rumbling and initially thought it was an earthquake, while another described a loud bang that felt "like a bomb blast".
More than 5,000 rescue workers from the National Disaster Response Force, army and other rescue teams were slowed by traffic- clogged streets and buildings packed on either side of the street.
The death toll is expected to rise.
Prime Minister Narendra Modi, in Washington for the Nuclear Security Summit, said on Twitter that he was monitoring the situation.
"Shocked and saddened by collapse of under-construction flyover in Kolkata," he tweeted. "My thoughts are with the families of those who lost their lives in Kolkata. May the injured recover at the earliest."
Kolkata is a city of stunning colonial architecture that was once India's capital. In recent years, it has seen a spurt of building, and yesterday's disaster triggered concerns about safety as builders rush to finish projects.
