* SSEC +0.6 pct, CSI300 +0.7 pct, HSI +0.5 pct
* PBOC resumes open market operation on Monday
* China regulator vows to punish 'giant crocodiles' in capital markets
SHANGHAI, Feb 13 (Reuters) - Chinese stocks opened the week on a firm footing on Monday and were track for the fourth straight day of gains, with sentiment boosted by strong commodities, while the Hong Kong market hit four-month highs thanks to capital inflows from the mainland.
China's blue-chip CSI300 index rose 0.7 percent, to 3,436.51 points at the end of the morning session, while the Shanghai Composite Index gained 0.6 percent, to 3,216.83 points.
Some good news over the weekend, including a rally in metals prices, supported the market, said Tian Weidong, analyst at Kaiyuan Securities in Xi'an.
He said liquidity concerns also eased somewhat as China's central bank injected 100 billion yuan into money markets on Monday after skipping open market operations for six trading days.
However, the market may be ripe for a correction after several days of gains, Tian said.
Chinese equities have been supported in recent weeks by signs of stabilising economic growth, though a turn by Beijing to tighter policy settings has restrained demand.
On Friday, China's top securities regulator vowed to apprehend law-breaking financial tycoons he called "giant crocodiles", which came after Chinese-born billionaire Xiao Jianhua disappeared in Hong Kong and a Chinese hedge fund manager Xu Xiang was sentenced to jail for market manipulation.
Shares of companies tied to Xiao fell in Shanghai on Monday, as Xiao's disappearance prompted media speculation that he has been abducted and taken to mainland China.
The tech-heavy start-up index shrugged off early losses and climbed to a one-month high by lunch break.
Most sectors advanced modestly by lunch break, with wine makers adding 4.5 percent.
In Hong Kong, the benchmark Hang Seng index added 0.5 percent, to 23,694.80 points, while the Hong Kong China Enterprises Index gained 1.2 percent, to 10,244.69 points.
The market was supported by rising southbound inflows through the Shanghai-Hong Kong Stock Connect, which used 24 percent of Friday's daily quota, compared with an average of less than 11 percent in January.
Most sectors firmed in the city at midday, but property developers contracted 0.5 percent after hitting a nearly 3-1/2-month high in the previous session.
Resource stocks added 1.5 percent, while an index tracking nonferrous metals prices in Shanghai rallied and hovered near a 3-1/2-year high.
Shares of Geely Automobile Holdings Ltd jumped 6.6 percent at midday, the first day that it became a constituent of the Hang Seng Index.
Reporting by Jackie Cai and John Ruwitch; Editing by Shri Navaratnam