China's property stocks have entered a technical bear market over worries that Beijing's efforts to prop up the sector are falling short of ending the retreat, as the nation’s government promises to buy unsold properties.

A Bloomberg Intelligence index of Chinese developer shares declined 3.3% on Thursday to push losses to nearly 21% from a mid-May high, Bloomberg reported.

Sunac China Holdings shares saw the biggest drop on Thursday, plummeting 12% to 0.146 euros. Real estate shares have declined as skepticism has brewed over a broad support package unveiled by China’s central government on May 17.

Investors initially cheered policies that include lower down-payment requirements for homebuyers, but they have since questioned their effectiveness in reviving demand and addressing a very high housing inventory, Bloomberg reported.

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They have also raised concerns over their size because a central bank program would spur bank loans worth 500 billion yuan ($69 billion), according to officials, thus covering only a small fraction of the value of China’s empty apartments.

New-home sales at the 100 biggest real estate companies dropped 33.6% from a year earlier in May, easing from a 45% decline in April, China Real Estate Information Corp. data showed, according to Bloomberg.

While the slight month-on-month pickup held up property shares earlier this week, worries over the long-term outlook later pushed investors to take profits.

Some investors wait for a clearer sales-recovery picture, while others seek indicators on major policy shifts that may be unveiled at the Third Plenary Session in July.

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