The bridge sagging incident in Mizoram which has claimed 17 lives was due to the collapse of a gantry which was being launched on the under-construction bridge over Kurung river, the Railways said Wednesday.

The Railways has constituted a high-level committee to probe the incident involving the under-construction bridge, one of the 130 bridges in the Bhairavi-Sairang New Railway Line project.

A Railways spokesperson said the gantry which collapsed was designed by STUP Consultant and proof checked by IIT Guwahati.

"High level enquiry committee has been constituted to investigate into the matter," the spokesperson said.

Gantries are heavy steel structures used to lift and support bridge segments or girders as they are placed while being supported by the bridge piers instead of the ground.

"The bridge did not collapse. It was a gantry which fell while it was being launched on the under-construction bridge," the spokesperson told PTI.

While Mizoram Chief Minister Zoramthanga referred to the incident as a bridge collapse, the Railways claimed that the part of the bridge which has already been constructed is still intact.

The Bairabi–Sairang line is a 51 km long from Bairabi to Sairang under the Northeast Frontier Railway zone of Indian Railways.

The rail line entails 130 bridges, 23 tunnels and four stations -- Hortoki, Kawnpui, Mualkhang and Sairang.

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