At least 137 people died in western India when a colonial-era pedestrian bridge packed with revellers collapsed into the river below, police said Monday.

Authorities said nearly 500 people were celebrating the last day of the Diwali festival on and around the nearly 150-year-old suspension bridge in Morbi when supporting cables snapped after dark on Sunday.

CCTV footage showed the structure in Prime Minister Narendra Modi's home state of Gujarat swaying -- with a few people apparently deliberately rocking it -- before it suddenly gave way.

The walkway and one fence crashed into the river, leaving the other side dangling in mid-air and hundreds of people in the water.

"I saw the bridge collapse before my eyes," said one witness who worked all night on rescue efforts, without giving his name.

"It was traumatic when a woman showed me a photo of her daughter and asked if I had rescued her. I could not tell her that her daughter had died."

Another witness named Supran said the bridge was "jam-packed".

"The cables snapped and the bridge came down in a split second. People fell on each other and into the river," he told local media.

News reports showed footage of people clinging onto the twisted remains of the bridge or trying to swim to safety in the dark.

Most Indians cannot swim and another Morbi resident, Ranjanbhai Patel, said he helped pull out those who had been able to reach the banks.

"As most of the people had fallen into the river, we were not able to save them," he said.

Local police chief P. Dekavadiya said that by Monday afternoon that the death toll had risen to 137. They included around 50 children, the youngest being a two-year-old boy.

One local MP, Kalyanji Kundariya, told media he had lost 12 family members in the accident, including five children.

The bridge over the Machchhu river, a popular tourist spot, had only reopened several days earlier after months of repairs.

'No certificate'

Authorities launched a rescue operation following the collapse, with boats and divers searching the river all night and on Monday.

The suspension bridge, 233 metres (764 feet) long and 1.5 metres wide, was inaugurated in 1880 by the British colonial authorities and made with materials shipped from England, reports said.

The Gujarat tourist department describes the "grand suspension bridge" about 200 kilometres (120 miles) west of the state's main city, Ahmedabad, as an "artistic and technological marvel".

Sandeepsinh Jhala, Morbi municipality chief officer, said that after the recent renovation, the bridge had not been issued a safety certificate.

District police have launched an enquiry against the contractor, Yadav said.

Reports said the work had been carried out by a unit of the Gujarat-based Oreva group, which describes itself as the world's largest clock manufacturer, and also makes lighting products and e-bikes. It could not immediately be reached for comment.

Modi, who was due to visit the site on Tuesday, said that he "may rarely have experienced so much pain in my life."

Moscow and New Delhi have enjoyed close relations for decades and the Kremlin said in a statement that Russian President Vladimir Putin sent his condolences.

Japan's Prime Minister Fumio Kishida said he was "deeply saddened" while Nepal, Bhutan and Britain also sent messages of support.

Accidents from old and poorly maintained infrastructure, including bridges, are common in India.

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

Five years earlier, at least 32 people perished when a packed bridge collapsed in the hill resort of Darjeeling.