Shanghai's key stock index tumbled this morning on concerns over Korean tension and the European debt crisis.

The benchmark Shanghai Composite Index dropped 2.8 percent, or 82.21 points, to 2,811.53. Turnover grew to 82.4 billion yuan (US$12.4 billion) from last Friday's 50 billion yuan.

The Shenzhen Composite Index, which tracks the smaller mainland market, was down 3.3 percent to 1,303.87.

South Korea prepares for a live fire artillery exercises near border today. It previously said that bad weather had delayed the start of the exercise.

Concerns over European debt crisis deepened after Moody's Investors Service slashed Ireland's credit rating by five notches to Baa1 from Aa2 last Friday.

Steel makers dropped on news that firms in the sector made an average 3.5 percent profit this year, ranking the worst among all sectors invested. Baoshan Iron & Steel Co fell 3 percent to 6.44 yuan. Wuhan Iron & Steel Co similarly lost 3 percent to 4.41 yuan.

Cement firms led the decliners. Anhui Conch Cement Co tumbled 6.9 percent to 27.61 yuan. Hebei Taihang Cement Co trailed 5 percent to 13.05 yuan.

Metal producers dropped following lower metal prices on a stronger US dollar. Jiangxi Copper Co was down 4.6 percent to 38.60 yuan. Aluminum Corp of China sank 3.2 percent to 10.05 yuan.