(Amends name of commission in fifth paragraph)
* HSI -0.1 pct, H-shares -0.5 pct, CSI300 +0.4 pct
* HK stocks fall on concern over political unrest
* Optimism lifts China index
* Nuclear power shares strong after NDRC support policy
By Chen Yixin and Donny Kwok
SHANGHAI/HONG KONG, Sept 25 (Reuters) - China shares maintained upward momentum on Thursday morning, rising on investor optimism about broad economic reforms and bolstered by a leap in nuclear power-related shares after the government announced sector-friendly policies.
At midday, the CSI300, an index of leading Shanghai and Shenzhen A-share listings, climbed 0.4 percent, while the Shanghai Composite Index gained 0.5 percent at 2,355.91 points.
"Investors are still confident that policy support and ongoing reform will bring benefits to the stock market. Even though the central bank has ruled out the possibility of broad policy easing, investors still believe targeted measures provide enough to support for the near term," said Du Changchun, an analyst at Southeast Securities in Shanghai.
Du and several other analysts have said the Shanghai Composite could, however, meet strong pressure around 2,400 points.
Nuclear power-related shares were among the biggest gainers after the National Development Reform Commission (NDRC), China's central planning agency, said that it planned to start four projects that would produce over 1,000 megawatts of nuclear power in coastal areas.
SUFA Technology Industry Co Ltd jumped to strike its 10 percent daily limit, while Shenzhen Woer Heat-Shrinkable Material Co Ltd gained 7.1 percent.
The benchmark Hang Seng Index lost steam after early gains as investors squared long positions on concerns over unrest in Hong Kong as pro-democracy activists prepare for a major protest in their "Occupy Central" campaign on Oct.1.
The Hang Seng Index was down 0.1 percent at 23,903.72 points. The China Enterprises Index of the top Chinese listings in Hong Kong dropped 0.5 percent.
"The momentum in Hong Kong failed to keep up with the mainland as participants started to stay on the sideline ahead of the upcoming big day... no one knows what will happen as Occupy Central begins to kick off," said Steven Leung, a sales director at UOB Kay Hian.
Leung said the downside risk was limited as the index had fallen 1,000 points from its peak earlier this month, and any further slide might draw buyers.
The blue chip index was down 0.1 percent at lunch break, but the Hang Seng Properties sub-index had gained 0.5 percent.
Local property stocks led the early gains with Hang Lung Property rising 1.9 percent and Sino Land Co advancing 1.1 percent, offsetting a slide in gaming stocks, such as Galaxy Entertainment and Sands China, which both were down more than two percent. (Additional reporting by Shanghai Newsroom; Editing by Simon Cameron-Moore)