* SSEC 0.9%, CSI300 1.0%, HSI 0.5%
* Trade war has limited impact on China markets - regulator
* HK->Shanghai Connect daily quota used 6.5%, Shanghai->HK daily quota used 3.5%
SHANGHAI, May 28 (Reuters) - China's major stock indexes extended gains on Tuesday as a chief financial regulator downplayed the impact of the trade war with the United States, and as foreign investors bought shares ahead of MSCI's weighting increase.
** The CSI300 index rose 1% to 3,674.14 points at the end of the morning session, while the Shanghai Composite Index gained 0.9% to 2,918.12 points.
** A trade war with the United States has had limited impact on China's financial markets and its effects will be "even smaller" in the future, Guo Shuqing, chairman, China Banking and Insurance Regulatory Commission, said in a interview with state television broadcast on Monday.
** If Sino-U.S. trade tensions further deteriorate, there is a possibility of marginal easing in China's fiscal and monetary policies, as Beijing could take counter-cyclical measures to fully hedge the negative impact and stabilize market expectations, China Galaxy Securities said in report.
** Besides, Beijing is further opening up its financial markets despite the trade war, which market participants expect could bring in more long-term foreign money to prop up its stock market.
** By the lunchbreak, foreign investors bought 4 billion yuan ($579.26 million) worth of A-shares via the Stock Connect linking Hong Kong and the mainland, reversing an eight-session selling streak through Monday.
** The first phase of MSCI's weighting increase of Chinese mainland shares will take effect after the market close on Tuesday.
** Global index provider MSCI is quadrupling the weighting of Chinese mainland shares in its global benchmarks later this year, a move it said might draw more than $80 billion of fresh foreign inflows to the world's second-biggest economy.
** The Hang Seng index added 0.5% to 27,422.98 points, while the Hong Kong China Enterprises Index gained 0.5% to 10,458.41 points.
** Around the region, MSCI's Asia ex-Japan stock index was firmer by 0.31%, while Japan's Nikkei index was up 0.39%.
** The yuan was quoted at 6.9061 per U.S. dollar, 0.13% weaker than the previous close of 6.8974.
** The largest percentage gainers in the main Shanghai Composite index were Gansu Dunhuang Seed Group Co Ltd , which gained 10.1%, followed by Anhui Liuguo Chemical Co Ltd, which rose 10.1% and Suzhou New District Hi-Tech Industrial Co Ltd, which climbed 10.07%.
** The largest percentage losses in the Shanghai index were Qingdao Topscomm Communication Inc, which lost 5.22%, followed by Kangmei Pharmaceutical Co Ltd, which lost 5.06% and Guizhou Changzheng Tiancheng Holding Co Ltd , which slipped 5.03%.
** So far this year, the Shanghai stock index is up 15.98%, while China's H-share index is up 2.7%. Shanghai stocks have declined 6.04% so far this month.
** The top gainers among H-shares were Guangzhou Automobile Group Co Ltd, up 6.83%, followed by Great Wall Motor Co Ltd, gaining 5.19% and Byd Co Ltd, up by 4.3%.
** The three biggest H-shares percentage decliners were China Mobile Ltd, which has fallen 1.33%, China Minsheng Banking Corp Ltd, which has lost 0.7% and CITIC Ltd, down by 0.6%.
** About 12.12 billion shares have traded so far on the Shanghai exchange, roughly 45.1% of the market's 30-day moving average of 26.89 billion shares a day. The volume traded was 19.67 billion as of the last full trading day.
** As of 0415 GMT, China's A-shares were trading at a premium of 26.72% over the Hong Kong-listed H-shares.
($1 = 6.9054 Chinese yuan)
(Reporting by Luoyan Liu and John Ruwitch, Editing by Sherry Jacob-Phillips)