SHANGHAI, Sept 8 (Reuters) - China stocks fell on Friday, as investor optimism toward the world's second-largest economy waned after the authorities' stimulus policy, while a weakening yuan pressured the stock market further.

Meanwhile, the Hong Kong stock exchange delayed trading in both the securities and the derivatives markets on Friday morning due to a black rainstorm warning.

** By the midday recess, the blue-chip CSI 300 Index was down 0.8%, while the Shanghai Composite Index lost 0.4%.

** Trade numbers on Thursday showed a possible stabilisation in China's downturn, but economists said China's economy is still at risk of missing Beijing's annual growth target of about 5%. Some of the recent easing measures may have little impact on the slowing economy, they added.

** China's yuan weakened to the lowest level since December 2007 on Friday, as the widening services trade deficit and yield gap with other economies, particularly the United States, affected capital flows and trade.

** Most sectors fell, with shares in property developers , energy companies, and media firms down between 1% and 2.5%.

** Semiconductor shares rose 0.8% on the launch of Huawei's Mate 60 Pro+ smartphone, which captured global attention for revealing the Chinese tech firm's success in beating back U.S. sanctions.

** Shenzhen Rongda Photosensitive & Technology Co jumped nearly 10% to lead the gains, while Semiconductor Manufacturing International Corp (SMIC) added 0.7%.

** Shares of Apple suppliers fell, following reports that China had widened curbs on use of iPhones by state employees. Luxshare Precision Industry Co dropped 3.4%. (Reporting by Shanghai Newsroom; Editing by Janane Venkatraman)