POSCO, South Korea\'s leading steelmaker, plunged on the local bourse on Friday on reports that an explosion at one of its furnaces took place earlier in the day. Shares of POSCO were trading at 380,000 won on the Seoul bourse as of 1:40 p.m., down 4.64 percent from the previous session\'s close. The steelmaker halted the operations of the furnace and there were no casualties, POSCO said. The explosion at the furnace in the port city of Gwangyang, 423 kilometers south of Seoul, did not lead to an overall production disruption, it said. The steelmaker said it was looking into the cause of the explosion at the furnace, which has an annual production capacity of 3.5 million tons. POSCO produced 33.7 million tons of steel last year.