At least 17 labourers working on a railway bridge being built across a ravine in India's eastern Mizoram state were killed when it collapsed on Wednesday, officials said, with others reported missing.

Video footage posted by Mizoram chief minister Zoramthanga showed a metal frame that had toppled off towering columns into a wooded valley below.

"Under construction railway over bridge at Sairang, near Aizawl collapsed today; at least 17 workers died," Zoramthanga, who uses only one name, said on X, formerly known as Twitter.

The Indian Express newspaper quoted a policeman as saying that 17 bodies had been recovered and "many others" were missing. It was not possible to immediately verify the reports of people missing.

"Rescue operations are underway and all possible assistance is being given to those affected," the office of Prime Minister Narendra Modi said.

Modi was "pained" by the accident and offered his "condolences to those who have lost their loved ones", his office said on X.

The government will pay some $2,400 to the next of kin of those killed, it said.

Mizoram is in the far east of India, bordering Myanmar.

People had "come out in large numbers to help with rescue", Zoramthanga said, adding he was "deeply saddened and affected by this tragedy".

Accidents on large infrastructure construction sites are common in India.