Ulsan: One worker was killed and another was feared dead among the seven still trapped after a boiler tower collapsed at a thermal power plant in the southeastern city of Ulsan, authorities said Friday.

According to Yonhap News Agency, during a rescue operation, one worker was pronounced dead due to cardiac arrest, as reported by firefighting authorities in Ulsan. The boiler tower collapsed Thursday at a power plant of the Ulsan branch of Korea East-West Power Co., a state-run utility company. Initially, nine workers had been reported trapped, but two were rescued earlier.

The collapsed tower was 60 meters tall and reportedly in the process of being dismantled using explosives. The trapped people are all presumed to be employees of a subcontractor.