* Hang Seng Index ends up 0.71%

* China Enterprises index HSCE rises 1.29%

* HSI financial sector sub-index gains 1.2%

Aug 17 (Reuters) - Hong Kong shares marked their highest close in nearly four weeks on Monday, tracking a regional rise after China's central bank provided more medium-term loans to the country's financial system.

** At the close of trade, the Hang Seng Index was up 178.92 points or 0.71% at 25,505.82, its highest close since July 21. ** The Hang Seng China Enterprises index rose 1.29% to 10,450.56. ** The sub-index of the Hang Seng tracking energy shares rose 1.4%, while the IT sector dipped 0.27%, and the financial sector ended 1.15% higher. ** China's central bank issued medium-term loans worth 700 billion yuan ($100.86 billion) to financial institutions on Monday, rolling over 550 billion yuan of such loans maturing in August and injecting a further 150 billion. It left borrowing costs unchanged. ** Shares of securities firms followed their counterparts on the mainland higher, after the Shenzhen Stock Exchange said on Friday that the first batch of companies registered for listing on Shenzhen's ChiNext start-up board under a revamped initial public offering system will make their debuts on Aug. 24. The move is expected to lift brokerage firms' valuations. ** China Merchants Securities Co Ltd jumped 13.19%. ** Geely Automobile Holdings Ltd, bucked the broader trend, falling 6.35% after the company trimmed its full-year sales outlook. ** China's main Shanghai Composite index closed up 2.34% at 3,438.80 points, while the blue-chip CSI300 index ended up 2.35%. ** Around the region, MSCI's Asia ex-Japan stock index was down 0.24%, while Japan's Nikkei index closed 0.83% lower. ** The yuan was quoted at 6.942 per U.S. dollar at 0807 GMT, 0.12% firmer than the previous close of 6.9501. (Reporting by Andrew Galbraith; Editing by Susan Fenton)