BEIJING -- Chinese shares plummeted at midday Monday following the United States' loss of its top-tier AAA credit rating from Standard & Poor's.

The benchmark Shanghai Composite Index tumbled 3.68 percent to 2,529.88. The Shenzhen Component Index slip 2.97 percent to 11,354.42.

Rating agency Standard & Poor's on Friday cut the US debt rating to AA+ with a negative outlook for the first time.