* CSI300 -1.6 pct; SSEC -1.4 pct; HSI flat
* Investors ignore fresh market-calming measures
* Weak August trade data does not impact trading
* Outstanding margin loans fall a 12th straight session
SHANGHAI, Sept 8 (Reuters) - China stocks fell more than 1 percent on Tuesday morning despite market-soothing measures announced overnight, as investors continued to sell shares amid economic uncertainty.
But index futures rose in tiny volume after regulators imposed tough trading restrictions. Some traders described the market as comatose, with futures prices unable to reflect bearish sentiment.
The CSI300 index fell 1.6 percent, to 3,198.34 points at lunch break, while the Shanghai Composite Index lost 1.4 percent, to 3,038.05 points.
Hong Kong stocks were almost flat.
Late on Monday, China said it would remove personal income tax on dividends for shareholders who hold stocks for more than a year, a move aimed at encouraging longer-term investment in equities instead of short-term speculation.
The announcement came hours after regulators proposed introducing a "circuit breaker" on China's flagship CSI300 index to help stabilise the market. Under the proposal, if that index rises or falls 5 percent before 2.30 pm, trading will be suspended for 30 minutes.
But investors appear unimpressed.
"The circuit breaker may help calm sentiment, but it doesn't change investors' attitude toward stocks," said Hou Yingmin, analyst at AJ Securities.
He added that the tax cuts offer little incentive to stock buyers because "investors prefer to stand on the sidelines due to the huge uncertainty they face."
Economic data released on Tuesday - which did not impact mainland markets - showed that China's economy remains weak. August exports fell a less-than-expected 5.5 percent from a year earlier, while imports declined by 13.8 percent, far more than anticipated.
Wang Feng, CEO of hedge fund manager Alpha Squared Capital, attributed persistent market weakness also to the accelerated pace of deleveraging.
Outstanding margin loans fell for the 12th consecutive session, to 975.4 billion yuan ($153.17 billion) on Monday, while regulators are also stepping up a clean-up of grey-market, securities-related lending activities.
Traders say government restrictions on shorting activities could be counterproductive, as investors who are not able to adequately hedge risks in the futures or options market have no choice but to unwind their positions in the cash market to reduce risks.
Stocks in China fell across the board.
In Hong Kong, the Hang Seng index was unchanged at 20,592.67 points, while the Hong Kong China Enterprises Index gained 0.7 percent, to 9,171.01. ($1 = 6.3681 Chinese yuan) (Reporting by Samuel Shen and Pete Sweeney; Editing by Richard Borsuk)