Water entered construction areas at the Tarbela 5th Extension Hydropower Project on Monday after a weak rock mass collapsed during excavation, prompting an emergency evacuation of workers.

The Water and Power Development Authority said the collapse occurred during work on the second bench connecting tunnel. Water from the intake pit entered the tunnel and the under-construction powerhouse area. WAPDA said all workers were evacuated safely, the intake-pit water had been drained and dewatering of the powerhouse had begun.

The authority said the main tunnel, powerhouse, tailrace culvert and switchyard had not been damaged, and reported no injuries or deaths. Officials and the contractor are assessing the site. A district administration official told Dawn there was no immediate threat of flooding downstream, while Swabi’s deputy commissioner warned that additional water released from the dam could increase the Indus River’s flow and urged people to avoid bathing, swimming and boating.

The incident comes as the 1,530-megawatt project is already facing delays. A government inquiry into an earlier cofferdam collapse at T-5 had assigned responsibility to the project’s contractor, consultant and employer, WAPDA. The project’s completion date had been pushed to June 2028.

The latest incident’s effect on the construction schedule is not yet clear. WAPDA says assessments are under way.