The agency that has been constructing a flyover, a portion of which came down crashing at Kantibhita, around 30 km from Siliguri under the Phansidewa block on Saturday, said that the around 25 meters of girders might have collapsed due to an “external hit” by a trailer or a container (lorry).

Meanwhile, police said they have registered a case. The around 780-metrelong under-construction flyover on National Highway-31- D is part of the 3000-km East-West Corridor ~ a fourlane expressway connecting Gujarat with Assam and passing through north Bengal.

The National Highways Authority of India (NHAI) has taken up the corridor project. The girders were set up around seven days ago. Engineers and officials of Larsen & Toubro (L&T) Limited, the construction agency, the NHAI, and state PWD visited the site on Sunday.

The Darjeeling district administration has already ordered a probe to ascertain the cause of the incident and halted the construction work. NHAI project director Ajit Kumar Singh also visited the site with engineers.

“Primarily, it appears that the girders collapsed due to a heavy hit by either a container or a trailer. All four girders collapsed together as they were tied together,” said L&T technical head, PK Guha, who is stationed in Mumbai. “Had there been a failure on the concrete, it would not have collapsed suddenly. In the case of concrete failure, cracks would appear first, while it will take time for the collapse,” Mr Guha added.

According to him, joint reports of the L&T, NHAI and PWD would be submitted to the district administration. Mr Guha said the probe would be based on three things-materials used for construction, the way of construction and design of the flyover.

He, however, ruled out allegations that low quality materials may possibly have been used there. “According to a preliminary study, there is no possibility of the company compromising with the materials and the quality of work. A team of PWD would look into the design part during its visit tomorrow. A thorough study will help us find out the reasons,” he said.

Mr Guha, however, said unlike other project sites, CCTV cameras were not installed there. “It could have helped us ascertain the possible cause,” he said.

According to him, it would take them at least two months to set up new girders.  The L&T and NHAI informed the police in writing about the incident separately on Saturday. Meanwhile, police registered a case following the complaint from a member of the Siliguri Mahakuma Parishad, Md Ainul Haque.

“Low quality work and lack of alertness led to the incident and it could have resulted in loss of lives and property. I am demanding a proper investigation into the incident and punishment for the guilty,” said Mr Haque, who is also the president of the Phansidewa block- I Trinamul Congress. “We received two separate written information from L&T and NHAI on the incident. Police have registered a case based on the complaint of Md Ainul Haque,” a police officer said.