Shares tumbled Friday on the Seoul stock exchange on mounting doubts over the eurozone's ability to tackle its debt crisis, according to dpa. The benchmark Kospi index shed 37.64 points, or 2 per cent, to close at 1,874.75. Declining issues outnumbered advancers 565 to 274. The main index of the technology-heavy Kosdaq market fell 1.05 points, or 0.2 per cent, to 507.60. On currency markets, the US dollar was quoted at 1,146.50 Korean won, after trading at 1.131.40 won Thursday.