* HSI -0.6 pct, H-shares -0.4 pct, CSI300 -0.6 pct
* Commodities sectors spiral downwards as physical markets sink
* China cement climbs on rising prices, declining inventories
* Lenovo rebounds after three straight daily losses
By Clement Tan
HONG KONG, April 16 (Reuters) - Hong Kong shares sank to a near five-month low on Tuesday, while mainland China markets lingered at their lowest since Christmas as a downward spiral for commodities counters extended into a fourth day for some.
Losses for Jiangxi Copper and Zijin Mining again came in robust volumes, standing out against broader bourse volumes in both Hong Kong and China that stayed way below their respective averages for the last month.
At midday, the Hang Seng Index was down 0.6 percent at 21,648.2, after earlier testing its 200-day moving average at about 21,462.1, also its lowest since November.
A close below this key long-term technical level on the Hang Seng Index could point to further losses ahead. The China Enterprises Index of the top Chinese listings in Hong Kong slipped 0.4 percent.
The Shanghai Composite Index and the CSI300 of the leading Shanghai and Shenzhen A-share listings each shed 0.6 percent to their lowest since Christmas, both headed for a fourth-straight daily loss.
"It's a sell-off, but not quite a panic," said Jackson Wong, Tanrich Securities' vice-president for equity sales. "There're actually some funds rotating into non-commodities sectors after losses in the last few days."
Jiangxi Copper tumbled 4.3 percent to its lowest since October 2011 in Hong Kong and 2.6 percent in Shanghai after Shanghai copper prices fell to an 18-month trough.
China's biggest gold miner Zijin Mining fell 3 percent in Hong Kong and 3.1 percent in Shanghai. Zijin is set for a fourth day of losses and has now lost 12.4 percent in Hong Kong and 10 percent in Shanghai in that time.
Chinese oil majors were broadly weaker. CNOOC Ltd slid 1.8 percent to its lowest since June. PetroChina shed 1.8 percent in Hong Kong and 0.2 percent in Shanghai.
PATCHES OF STRENGTH ABOUND
Chinese property A shares were again strong after Monday's underwhelming data for first quarter GDP growth eased some concerns about property tightening. March home price data is due on April 18.
Further buoying sentiment, a front-page editorial in the official China Securities Journal on Tuesday said the central government should fine tune policy adjustments in response to slowing economic growth but should be cautious about using interest rates and or exchange rate tools.
China Vanke rose 1.9 percent in Shenzhen but remained bound in the range it has traded since the start of March when the central government announced guidelines for more sector curbs.
Chinese building materials producers were also strong. Anhui Conch Cement rose 0.9 percent each in Hong Kong and Shanghai as cement prices in the mainland continued to rise and inventories dropped to a four-month low, according to Nomura.
Chinese personal computer maker Lenovo Group is headed for its first daily gain in four days, having rebounded 1.4 percent at midday from Monday's 4-1/2-month closing low in Hong Kong.