Three people were injured, one critically, on Sunday when a concrete slab being laid on the Lucknow Metro rail route here collapsed, police said.
The accident took place at Sujanpura near the Alambagh bus station.
The injured have been admitted to a hospital where the condition of one of them was said to be critical. Others were being treated for non-life threatening injuries.
Metro spokesperson Amit Kumar Srivastava said the concreting collapsed at the station site. He said only one worker was injured.
District officials, however, said an auto-rickshaw driver and a friend were also hurt in the accident.
Lucknow District Magistrate Raj Shekhar told IANS that the National Disaster Relief Force (NDRF) had reached the accident site to help with rescue operations.
An inquiry has been ordered into the accident.