The benchmark Shanghai Composite Index and the Shenzhen Composite Index, which tracks stocks on China's second exchange, both opened more than two percent higher.
But minutes later they reversed the gains, with the Shanghai index down 0.68 per cent, or 21.15 points, to 3,103.85, and the Shenzhen indicator dropping 1.80 per cent, or 35.22 points, to 1,922.87.
"After the plunges in the previous days, market sentiment has changed," Haitong Securities analyst Zhang Qi told AFP.
Global investors have been alarmed by slowing growth in the world's second-largest economy, which is expected to have expanded in 2015 at its slowest pace in a quarter of a century. Official data on fourth-quarter and annual growth is due to be released later in January.
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Today's swings came after the China Securities Regulatory Commission (CSRC) late Thursday said it was shelving the "circuit breaker", which it had introduced at the beginning of the year.
But dealers said the system instead heightened selling pressure from traders who wanted to avoid being stuck with shares they did not want to hold.
"After weighing advantages and disadvantages, currently the negative effect is bigger than the positive one," the CSRC said in a statement.
"Therefore, in order to maintain market stability, CSRC has decided to suspend the circuit breaker mechanism."
The People's Bank of China (PBoC) set the daily reference rate at 6.5636 to the greenback, according to the China Foreign Exchange Trade System.
It was up 0.02 per cent from Thursday, when it was set at its lowest level in nearly five years.
China limits the yuan to rising or falling two percent on either side of the reference rate.
The eight days of falls revived concerns over the currency of the world's biggest trader in goods.
China has pledged to make the value of the yuan more flexible and market-oriented, and the International Monetary Fund has announced the unit will join its elite reserve currency basket.