SHANGHAI: The key mainland stock index yesterday soared 9.29 percent, the biggest one-day jump in six years, as investor sentiment was boosted by the government lowering of stamp duty.

The slashing of trading tax from 0.3 percent to 0.1 percent, effective yesterday, was widely seen as another government effort to lift the stock market from the doldrums it has been in for six months.

It followed the introduction of trading rules last Sunday to mitigate the impact of an expected flood of previously non-tradable shares after the lock-in period, which could greatly depress the market.