A selloff in Chinese property stocks intensified Thursday, as concern mounted about the effects of an official campaign to rein in the sector that has already sparked turmoil at China Evergrande Group.

The Lippo Select HK & Mainland Property Index dropped 4.9%, closing at its lowest level in more than four years, FactSet data showed. The drawdown in property shares helped pull Hong Kong’s flagship Hang Seng Index down about 1.5% to 24667.85, the benchmark’s lowest closing value of 2021.

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A selloff in Chinese property stocks intensified Thursday, as concern mounted about the effects of an official campaign to rein in the sector that has already sparked turmoil at China Evergrande Group.

The Lippo Select HK & Mainland Property Index dropped 4.9%, closing at its lowest level in more than four years, FactSet data showed. The drawdown in property shares helped pull Hong Kong’s flagship Hang Seng Index down about 1.5% to 24667.85, the benchmark’s lowest closing value of 2021.

The 52-stock Lippo Select index is mostly made up of real-estate companies based in mainland China. Including Thursday’s move, it has dropped 23% so far this year, as Beijing has piled pressure on real-estate developers in an attempt to cool the country’s property market.

Some investors worry that Beijing’s deleveraging push will mean more developers run into trouble, and that this could also drag down their associated property-management companies, said Lung Siufung, an analyst with CCB International Securities.

“Some people are losing their nerve,” Mr. Lung said. He said economic data released Wednesday, which also pointed to weakness in the property market, was another factor.

The fact that Beijing has so far refrained from offering help to Evergrande has exacerbated the anxiety, he added, although he said Chinese authorities were unlikely to allow a disorderly unwinding of real-estate debts. On Tuesday, Evergrande said it had hired financial advisers, moving closer to a potential debt restructuring.

The situation at Evergrande has fostered “extreme negative sentiment” toward the whole sector, said William Shek of Zeal Asset Management Ltd., a Hong Kong-based hedge-fund management company.

Both highly indebted companies and those with stronger balance sheets were caught up in Thursday’s selling, with the junk-rated Guangzhou R&F Properties Co. losing 12% and investment-grade-rated peer Shimao Group Holdings Ltd. falling 10%.

Evergrande dropped a further 6.4% and China Vanke Co. lost 3%, while property companies listed in mainland China also declined.

Property-management companies were hit as well. These companies specialize in taking care of apartment complexes and helping residents with issues such as child care, groceries and repairs. The sector has blossomed in recent years, with many developers listing property-services units.

The 30-constituent Hang Seng Property Service and Management Index fell 7.2%, closing at its lowest level since its launch in April. Sector heavyweight Country Garden Services Holdings Co. retreated about 11%.

Mr. Shek at Zeal said that while sentiment was negative on the whole property sector, the property-management companies weren’t directly affected by the government push and their earnings had been very good. “Some of this selling is likely overdone,” he said.

Write to Xie Yu at Yu.Xie@wsj.com