* SSEC -0.1 pct, CSI300 -0.3 pct, HSI -0.1 pct
* China's Politburo pledges to prevent 'systemic' financial risks
* China's second-half GDP growth seen at around 6.7 pct - official think tank
SHANGHAI, July 25 (Reuters) - China stocks eased on Tuesday as blue chips paused for breath after their recent strong rally, and as a fresh pledge by Beijing to prevent 'systemic' financial risks reignited fears of tighter regulations.
The CSI300 index fell 0.3 percent to 3,731.40 points by the end of the morning session, while the Shanghai Composite Index lost 0.1 percent to 3,246.04 points.
China's Politburo, the Communist Party's top decision-making body, said Beijing will implement a "proactive" fiscal policy and "prudent" monetary policy in the second half of the year, the official Xinhua news agency reported on Monday.
China will also strengthen coordination of financial regulation, stabilise the property market and prevent systemic financial risks, according to a statement following the meeting chaired by President Xi Jinping.
Regulators issued a flurry of measures earlier in the year to crack down on riskier forms of financing, but paused recently to review if they were impacting economic growth.
After second-quarter growth exceeded expectations, many analysts expect the government has room to keep those administrative measures in place for at least the rest of the year, with a possibility of more targeted action if risks appear to flare again.
China's economy is likely to grow at an annual rate of around 6.7 percent in the second half of 2017, slowing slightly from the first half of the year, the State Information Center (SIC) said on Tuesday.
China's mutual fund managers remained overweight on industry heavyweights in the second quarter, Changjiang Securities wrote in a report, adding sector leaders are more attractive for their business performance and valuations.
For example, shares in China Merchants Bank, the nation's largest retail bank, have leapt 47 percent so far this year, far outperforming other big-cap peers.
Shares of the bank rose 0.4 percent on Tuesday, after it reported late on Monday that first-half profits rose more than 11 percent.
The country's mutual funds stepped up their holdings in mainboard shares in the past three months, while cutting their exposure to start-ups to the lowest level since the fourth quarter of 2013, the brokerage wrote.
The trend tallied with a retreat from start-up companies, with the start-up board index losing 13.9 percent so far this year, versus a gain of 12.7 percent in the blue-chip CSI300 index.
Most sectors lost ground in the morning, with real estate and material shares leading the decline, while gains were seen in banking plays.
Hong Kong's benchmark Hang Seng index was marginally lower at 26,816.93 around mid-day as losses in energy and telco sectors offset gains in technology and consumer cylicals shares.
The benchmark had ended 0.5 percent higher at two-year high on Monday.
The Hang Seng China Enterprises Index, that tracks the performance of China companies listed in Hong Kong, was 0.3 percent lower at 10,793.42.
"The market is still good, but what we see is with too much short-term setup it still may be facing some profit-taking pressure," said Linus Yip, chief strategist at First Shanghai Securities.
"The market overall still has the chance to test higher. The Hang Sang index may have the chance to go to the 27000 level or even test the 27200 point."
Sinopec's 1.7 percent decline was the biggest drag on the HSI and the energy sector.
The oil and gas explorer and refiner reported a 5 percent decline in its half-year crude oil production last week.
A 0.3 percent slide in China Mobile shares weighed on the telecom sector.
Technology sector bellwether Tencent Holdings was the top gainer on the benchmark, adding about 0.4 percent.
Speakers maker AAC Technologies, a much smaller sector peer of Tencent's, was among the top gainers too with its near 1 percent rise.
Reporting Luoyan Liu, Rushil Dutta and John Ruwitch; Editing by Kim Coghill