* CSI300 -0.2 pct; SSEC -1 pct; HSI +1.5 pct
* Central bank's injection hints of monetary easing
* China Eastern Airlines falls after Delta agrees to buy stake
HONG KONG, July 28 (Reuters) - China stocks were lower by midday on Tuesday, in volatile conditions, even as Beijing pledged to lend further support after stocks sank 8 percent in the previous session, raising concerns about stability in the world's second-biggest economy.
Chinese regulators said they were prepared to buy shares to stabilise the stock market, while the central bank injected cash into money markets and hinted at further monetary easing.
"Retail investors' confidence in the mainland market is very weak. They prefer to stay away from the market after liquidating their position," said Steven Leung, a director from UOB Kay Hian in Hong Kong.
The CSI300 index fell 0.2 percent, to 3,810.65 points at the end of the morning session, while the Shanghai Composite Index lost 1.0 percent, to 3,688.48 points. The indexes were down 5 percent earlier.
China CSI300 stock index futures for August fell 1.5 percent, to 3,703.4, some 107.25 points below the current value of the underlying index.
The Hang Seng index added 1.5 percent, to 24,721.29 points. The Hong Kong China Enterprises Index gained 0.4 percent, to 11,275.42.
The People's Bank of China said on Tuesday it would inject 50 billion yuan ($8.05 billion) into money markets in its biggest liquidity boost since July 7, near the trough of the last market sell-off.
Nomura said in a research note on Tuesday that there was little incremental change in Chinese economic fundamentals, with the weak flash Caixin PMI for July and industrial profit growth for June mainly reflecting the negative impact of the last sell-off in A shares.
"On the positive side, hard activity data including industrial production, retail sales and investment have started to pick up in 2Q15, suggesting the real economy is improving," Nomura said.
The index measuring price differences between dual-listed companies in Shanghai and Hong Kong stood at 136.66.
A value above 100 indicates Shanghai shares are pricing at a premium to shares in the same company trading in Hong Kong, and vice versa.
The northbound quota for the Hong Kong-Shanghai Stock Connect, currently set at 13 billion yuan, saw net inflows of 1.65 billion yuan.
Total volume of A shares traded in Shanghai was 36.73 billion shares, while Shenzhen volume was 25.36 billion shares.
Total trading volume of companies included in the HSI index was 1.3 billion shares.
Small caps also fell. Shenzhen's start-up board ChinNext lost 2.1 percent.
In Hong Kong, shoe retailer Belle International led gains in the blue chip index, surging 4.5 percent, while PetroChina led the surge in the Chinese enterprises index in the territory, up 4.4 percent.
China Eastern Airlines' Hong Kong shares fell 4 percent on dilution concerns after Delta Air Lines agreed to buy a 3.55 pct stake in China Eastern for $450 million. (Reporting by Donny Kwok; Editing by Jacqueline Wong)