At least 15 people were killed and more than 70 trapped after a flyover under construction collapsed in the eastern Indian city of Kolkata Thursday, news reports said.
Several cars and rickshaws parked under the bridge were crushed along with at least one bus when around 100 metres of the flyover fell, witnesses were quoted as saying by India Today news channel.
"One girder seems to have fallen and then another collapsed," said KP Rao, spokesman for construction company IVRCL. "We are not sure exactly what the problem was."
Rescue efforts were under way to reach those trapped, said Mamata Banerjee, chief minister of West Bengal state.
Two units of the National Disaster Response Force were rushed to the site and cranes were being used to lift debris. News footage showed some cars being lifted out from the rubble.
"We do not have figures of how many people have died, but at least 20 injured people have been admitted to nearby hospitals," an official at the Kolkata Police control room told dpa.
Many people had head and neck injuries, and several suffered burns when their vehicles caught fire, police said.
The death toll of 15 was reported by local news channel ABP Ananda.
"At least two of our engineers are missing," Rao said from IVRCL headquarters in Hyderabad. "We must have had 30 to 40 people working on the site," he said in remarks quoted by several media.
The army has also been called in to help, said Banerjee, who called off an election rally to visit the site in the state capital. Around 300 army engineers and medical personnel were deployed, reports said.
Residents formed a human chain to keep onlookers back from rescue operations, reports said.
"Shocked & saddened by collapse of under construction flyover in Kolkata," Primer Minister Narendra Modi posted on Twitter.
Construction on the flyover started in 2008 but had stopped and started several times amid apparent financial trouble suffered by IVCRL, according to an India Today report.
The flyover was almost the width of the road, and passed close to rows of three- and four-storey houses and shops on both sides, in an extremely congested area in the north of the city.