CHENNAI: The beam collapse at the Metro Rail construction site in Manapakkam on Thursday night happened after one of the supporting A-frames slipped away, said Chennai Metro Rail Limited.

The massive structures, each measuring 40 feet (12 feet) in length, crushed a motorcyclist who was passing under the beam right at that time.

The large beams (girders) were erected a week ago near the L&T head office main gate in Manapakkam. They collapsed "when one of its supporting A-frames gave way by slipping", CMRL said in a statement.

It added that an investigation would be conducted to ascertain the cause of the collapse.

"It's with regret that we confirm one fatality from the incident. A thorough investigation is forthcoming," the Chennai Metro Rail added in a statement.