(Reuters) - Hong Kong and China shares suffered their sixth-straight losses on Thursday as resource-related stocks took a beating after a broad commodities selloff overnight deepened already-hefty risk aversion in global markets.

The Hang Seng Index fell 1.8 percent, to 18,026.8 points, while the China Enterprises Index of the top mainland firms listed in Hong Kong declined 2.1 percent.

The Shanghai Composite Index also slumped 2.1 percent. It finished at 2,180.9 points, breaking below yet another chart support and sinking to a fourth-straight 33-month closing low.

Wednesday's tumble in world oil prices -- by more than 4 percent -- spawned Chinese oil and resources stocks to fall steeply in big volumes.

Alan Lam, Julius Baer's Greater China equity analyst, said those plunges were related to the international markets and the change in the OECD's stand on oil supply issues.

Stocks of upstream oil players, such as CNOOC, have very high correlation to oil prices and suggest a medium-to-long term market forecast on oil prices, he said.

Lam also said the A-share market was under some redemption pressures this week with retail investors jittery and having poor market expectations. The Shanghai Composite is down 5.8 percent so far this week.

China Life Insurance, the mainland's biggest life insurer and seen as a barometer of the mainland A-share stock market, was Shanghai's top drag, slumping 8.9 percent.

In a note on Thursday, BNP Paribas China equity strategists said they expect the mainland A-share market to underperform H-shares in 2012 because among three listed reasons, fund raising activities will be stronger in the mainland in the near term.

RISK AVERSION SPIKES

In Hong Kong, CNOOC Ltd, slumped 4.6 percent and was the top drag on the Hang Seng Index. It is down more than 6.5 percent this week.

Yanzhou Coal led losses among coal stocks. It dived 5.8 percent in Hong Kong in volume more than twice its 30-day average, and it slumped 7.3 percent in Shanghai.

China's biggest gold miner, Zijin Gold Mining Group , lost 3.9 percent in Hong Kong and 5 percent in Shanghai.

Underscoring the adverse sentiment on Thursday, two of Hong Kong's biggest recent initial public offerings slumped in their trading debuts after unfavourable performances on the gray market the day before.

Chow Tai Fook Jewellery Group Ltd, the world's biggest jewellery retailer, and New China Life Insurance fell about 8.4 and 10 percent from their offering price after the companies raised a combined $3.9 billion.

New China Life Insurance, the mainland's third-largest life insurer, will make its Shanghai listing debut on Friday.