Seven workers were killed and three remain missing after a large volume of water and debris entered the tail race tunnel of the Vishnugad-Pipalkoti Hydroelectric Project in Uttarakhand on Thursday evening, according to THDC India Ltd.At the time of the incident on August 13, concrete lining work was underway at chainage 1,230 metres, where 22 workers deployed by the principal executing agency, Hindustan Construction Company, were working, the company said in a statement.Twelve workers have been rescued while one injured worker has been discharged after treatment, THDC, which is developing the project, said.Joint teams from THDC India, Hindustan Construction Company, the National Disaster Response Force, State Disaster Response Force, Central Industrial Security Force and the district administration are conducting search and rescue operations for the missing workers.Equipment and other resources have been deployed to remove water and debris from the tunnel and enable rescue teams to move safely.Senior THDC management officials, including the managing director, are at the site overseeing the operation, it said.THDC said a detailed assessment of the causes and circumstances of the incident will be undertaken in coordination with the competent authorities and agencies.