* HSI down 1 pct, H-shares fall 1.8 pct, CSI300 lose 3.3 pct
* Beijing's Friday move will "freeze" market near term: UBS
* Vanke, Poly Real Estate A-shares down maximum 10 pct
By Clement Tan and Yimou Lee
HONG KONG, March 4 (Reuters) - China's CSI300 share index could post their worst daily loss in two years on Monday, deepening losses in Hong Kong, after Beijing hit the mainland property sector with harsher-than-expected tightening measures to curb housing costs.
After markets closed on Friday, the State Council demanded an increase in required down payments and loan rates for buyers of second homes in cities where prices are rising too quickly. The announcement came ahead of the start of China's annual parliamentary meetings on Sunday.
At 0325 GMT, the Hang Seng Index was down 1 percent at 22,648.5. The China Enterprises Index of the top Chinese listings in Hong Kong fell 1.8 percent.
In the mainland, the CSI300 of the top Shanghai and Shenzhen A-share listings was down 3.6 percent, set for its worst day since January 2011. The Shanghai Composite Index was down 2.7 percent.
The property sector took a battering, with the Shanghai property sub-index down 8.7 percent and the Hong Kong properties sub-index dropping 2.4 percent.
"Friday's evening announcement was very significant and was beyond the expectations of many in the market," said Hong Hao, chief equity strategist at Bank of Communication International Securities.
"We are in a high risk zone now. I wouldn't advise clients to add risk in the near term, since property is a huge sector, so this will have an effect on construction materials and equipment as well," Hong added.
China Vanke was down by the maximum daily limit of 10 percent in Shenzhen. If Monday's losses are maintained by the close of trade, persist, it would be the worst daily loss for the country's largest developer by sales since August 2009.
Poly Real Estate was also down 10 percent in Shanghai. In Hong Kong, China Resources Land sank 7.5 percent to its lowest this year.
UBS analysts downgraded their target prices by an average of 13 percent for 12 Hong Kong-listed Chinese developers they cover, expecting new measures to "freeze" the entire market and delay the originally planned sales schedules in the near term.
China's property market has been rife with speculation about what the country's new leadership may do to curb rising home prices in the lead up to this week's annual parliamentary meetings.
The annual Chinese People's Political Consultative Conference began on Sunday and the National People's Congress, where Xi Jinping is expected to be confirmed as president, starts in Beijing on Tuesday.