* Hang Seng Index down 0.3 percent, off 5.3 percent for week
* Shanghai eases, banks weigh on RRR rise report
* A- vs H-share premium at 8-mth high as Shanghai outperforms
* HKEx shares under pressure amid global exchanges mergers (Updates to midday)
By Vikram S.Subhedar and Chen Yixin
HONG KONG/SHANGHAI, Feb 11 (Reuters) - Hong Kong shares edged lower on Friday, with the benchmark index on track for its worst weekly decline in nine months, as HSBC and other blue chips offset gains in other large caps.
The benchmark Hang Seng Index was down 0.28 percent at 22,644.39 by the midday trading break, slipping below a trendline support on the charts that had held since May last year and raising the risk of a retest of the December 2010 low around 22,400.
The Shanghai Composite Index was little changed by midday as worries over further monetary tightening hit financial counters, but gains in sectors seen benefitting from government support helped support the index.
The Shanghai Composite, which started the year on a weak note following a 14 percent slide last year, has outperformed the Hang Seng Index this month.
That has lifted the valuation premium at which A shares trade over their Hong Kong-listed peers to the highest since May 2010, with some analysts predicting mainland markets to continue to outperform this year.
Hong Kong's market has taken a hit as most North Asian markets succumbed to profit-taking, with South Korea's KOSPI dropping 4.3 percent and Taiwan's TAIEX down mor than 6 percent.
With emerging market "dominoes" continuing to fall, clients are becoming increasingly nervous and are buying downside protection through put options, said a Hong Kong-based trader at a large U.S. investment bank.
"The S&P remains vulnerable at 1320, it needs to correct to even think about buying," said the trader.
In Hong Kong, HSBC Holdings Plc, which have supported the broader market through the week, fell 1.2 percent and offset recovery in certain other large caps such as Tencent Holdings Ltd and Li & Fung Ltd.
Hong Kong Exchanges & Clearing Ltd extended Thursday's heavy loss, falling 1.2 percent amid a flurry of merger activity among global exchanges.
SHANGHAI LITTLE CHANGED
Chinese economic data for January due next week is expected to show that lending surged and inflation accelerated, prompting concern among some investors that the central bank could take more steps to control money supply.
"Worries over further tightening after key economic data are making investors cautious," said Xu Yinhui, senior analyst at Haitong Securities in Shanghai. "But some sectors are getting support from news or policy. That may limit the drop in the index."
Almost all of the 16 banks listed in Shanghai and Shenzhen fell after an official newspaper reported that the central bank had imposed punitive reserve requirement measures on some small and medium-sized domestic banks.
Agricultural Bank of China Ltd, among the most active shares in the Shanghai market, slipped 0.4 percent. Bank Of China Ltd eased 0.6 percent. The financial sub-index fell 0.5 percent.
The benchmark Shanghai Composite Index was at 2,815.6 points, after rising 1.6 percent on Thursday. The index is now up 0.6 percent since reopening after the Lunar New Year holiday.
Rare earth companies outperformed after official media reported that China had created a "state planning" zone covering the country's biggest rare earth mines in a move to cut production of the vital mineral elements used for numerous high-tech goods.
Rising Nonferrous Metals Share Co Ltd rose 1.5 percent, while Xiamen Tungsten Co Ltd was up 1.8 percent. (Editing by Chris Lewis)