* Hang Seng Index up 0.5 pct, futures expiry adds volatility
* Shanghai weaker, investors continue to dump B shares
* Financials support as Ping An, AgBank results impress
* Coal, gold producers rise on results, bullion prices (Updates to midday)
By Vikram Subhedar and Yixin Chen
HONG KONG, April 28 (Reuters) - Hong Kong shares were slightly by midday Thursday, supported by financials after impressive results from top insurer Ping An and Agricultural Bank of China, the first of China's big banks to report quarterly results.
A weak showing in Shanghai markets, however, where investors dumped speculation-driven B shares for a second session, kept gains in check.
Hong Kong's Hang Seng Index was up 0.5 percent at the midday trading break, holding above the 24,000-level but remaining within a narrow trading range in place for just over two weeks. The index's 2011 intraday high of 24,468.6 remained a strong near-term resistance point, traders said.
The Shanghai Composite Index ended the morning down 0.1 percent as the index of dollar-denominated B shares extended its decline for a second day, down as much as 7 percent earlier in the session.
"The pick-up in volume on the B-share index probably gave a lot of domestic investors a chance to cash out," said a Hong Kong-based trader, referring to the low volumes seen in B-share trading that make exiting positions difficult.
The broader market was little impacted by the slide and found support from banking counters on earnings optimism.
Three of China's biggest state-controlled banks are expected to report robust first-quarter earnings on Thursday, a day after Agricultural Bank of China Ltd set the tone with a 36 percent jump in first-quarter net profit. [ID:nL3E7FS04W]
"Now the index has support from stocks that have good results, such as banks," said Xiangcai Securities analyst Cheng Yi in Shanghai.
AgBank shares rose 1.9 percent in Hong Kong and 2.8 percent in Shanghai, underscoring investors' focus on earnings with companies reporting weak numbers seeing shares selling off.
STEELMAKERS WEAK
Steelmakers continued to be weak, with the biggest losers being Laiwu Steel Corp , down by its 10 percent daily limit, and Jinan Iron and Steel Co Ltd , which dropped 9.3 percent.
A massive run-up in shares of the two companies was seen over the past two weeks on speculation over their planned merger.
Angang Steel Co Ltd was down 0.8 percent in Hong Kong after reporting a 93.8 percent plunge in first-quarter profit. Angang has fallen more than 10 percent since April 14 after it warned of weak results due to escalating raw materials costs.
Rising commodities prices were seen lifting coal and gold producers, with China Coal Energy Co Ltd gained 4.8 percent in Hong Kong after it reported a rise in first-quarter profit. [ID:nH9E7F602I]
China Coal was the top performer on the China Enterprises Index in Hong Kong, followed by gold mining company, Zijin Mining Group Co Ltd , which rose 2.4 percent.
Inner Mongolia Yitai Coal Co Ltd , the biggest stock on the B-share index, fell 2.9 percent however amid the slump on the market.
Shanghai's B-share Index of dollar-denominated stocks was down 4.1 percent by midday after falling more than 7 percent in early trading. The Shenzhen B-share index of Hong Kong-dollar denominated shares fell 2.8 percent.
Rumors ranging from the introduction of an international board in Shanghai to the unveiling of a capital gains tax have been cited over the past two days as fuelling the decline in B shares.
A tax official told Reuters on Thursday that China was unlikely to start taxing investors on their capital gains any time soon. [ID:nL3E7FS0AC] ($1 = 6.512 yuan) (Reporting by Vikram Subhedar; Editing by Chris Lewis)