This photograph shows the site of an under-construction railway bridge that collapsed in Sairang town on Wednesday. AFP

The incident took place in Sairang, a town around 20 kilometres northwest of Mizoram state capital Aizawl — an outlying pocket of the country near the border with Myanmar.

According to railway and police officials, 22 bodies have been recovered so far. Rescue operations were on to recover the remaining four bodies from under the collapsed steel structure. The railway bridge was under construction over the Kurung River connecting Bairabi (near southern Assam) to Sairang, 10km away from Mizoram capital Aizawl.

Prime Minister Narendra Modi, Union Home Minister Amit Shah, Railway Minister Ashwini Vaishnaw, many chief ministers of the northeastern states and top leaders have expressed their deep anguish over the mishap.

Video footage shared by Mizoram Chief Minister Zoramthanga showed a metal frame that had toppled off towering columns into a wooded valley below. "Deeply saddened and affected by this tragedy," he wrote on X, formerly known as Twitter.

Zoramthanga, who uses one name, added that he was grateful that people had "come out in large numbers to help with rescue operations."

Forty labourers had been working at the site, according to the Northeast Frontier Railway. An employee of the agency, who requested anonymity as he was not authorised to talk to the media, said 22 bodies had been recovered from the wreckage. Another four people were still missing, he added.

A committee has been set up to investigate the cause of the accident.

"Rescue operations are underway and all possible assistance is being given to those affected," the office of Prime Minister Narendra Modi said. Modi, who is now in Johannesburg for BRICS Summit, was "pained" by the accident and offered his "condolences to those who have lost their loved ones", his office added. The government will pay around $2,400 to the next of kin of those killed, it said.

Railways Minister Ashwini Vaishnaw also announced separate compensation for those killed or injured in the accident.

Building and construction collapses are common during India's June-September monsoon season, with old and rickety structures buckling under days of non-stop rain.

At least 20 workers were crushed to death in western India this month when a crane collapsed above an under-construction expressway outside the financial capital Mumbai.

Last year, at least 137 people were killed when a pedestrian bridge collapsed in Gujarat state, sending hundreds of people tumbling into a river or clinging to the wreckage while screaming for help in the dark.

The collapse of a flyover onto a busy street in Kolkata killed at least 26 people in 2016.

In 2011, at least 32 people were killed when a bridge packed with festival crowds collapsed near the hill town and popular tourist destination of Darjeeling.

And less than a week later, around 30 people were killed when a footbridge over a river in the northeastern state of Arunachal Pradesh collapsed.