The CSI300 index fell 2.2 per cent to 3,288.80 points at the end of the morning session, while the Shanghai Composite Index lost 2.4 per cent to 3,109.95.
China CSI300 stock index futures for January fell 2.4 per cent, to 3,256, 32.80 points below the current value of the underlying index, suggesting investors see further losses.
"The market is still a bit unstable," said Xiao Shijun, an analyst at Guodu Securities in Beijing.
"Following the big move in the yuan last week, most A-shares are still under a fair amount of pressure."
China's central bank allowed the yuan to weaken by over 1.5 per cent against the dollar in the first week of 2016, its biggest currency move since mid August when a devaluation rattled world markets.
The yuan strengthened marginally against the dollar on Monday after the central bank said a firmer midpoint reference rate for the second session in a row.
Some traders believed the stronger official setting may signal the latest jolt of depreciation is over for now, though others said downward pressure on the currency will persist as the economy continues to slow.
December inflation data on the weekend added to investors' concerns.
China's consumer inflation barely edged up in December while companies' factory-gate prices continued to fall, adding to concerns about growing deflation risks.
In Hong Kong, the Hang Seng index dropped 2.5 per cent to 19,952.63 points, while the Hong Kong China Enterprises Index lost 3.5 percent, to 8,539.73.
The index measuring price differences between dual-listed companies in Shanghai and Hong Kong stood at 143.47.
A value above 100 indicates Shanghai shares are pricing at a premium to shares in the same company trading in Hong Kong, and vice versa.
The northbound quota for the Hong Kong-Shanghai Stock Connect, currently set at 13 billion yuan, saw net outflows of 0.25 billion yuan.
Total volume of A shares traded in Shanghai was 14.62 billion shares, while Shenzhen volume was 14.58 billion shares.
Total trading volume of companies included in the HSI index was 1.0 billion shares.
© Thomson Reuters 2016