Chinese shares plunged more than seven percent on Friday as margin traders closed positions and concerns over market overvaluation mounted, dealers said.

The benchmark Shanghai Composite Index slumped 7.40 percent, or 334.91 points, to 4,192.87 on turnover of 787.8 billion yuan ($128.9 billion). The Shanghai market lost 6.37 percent over the week.

The Shenzhen Composite Index, which tracks stocks on China’s second exchange, plummeted 7.87 percent, or 213.75 points, to 2,502.96 on turnover of 555.1 billion yuan. It dropped 8.72 percent for the week.