China has announced it is investigating several executives at state-owned property companies, in another blow to a key sector already struggling with slowing sales, angry customers and heavily indebted developers.

Authorities said in separate notices on Tuesday that they were investigating Zhuang Yuekai, chairman of C&D Real Estate, and Shi Zhen, chairman of C&D Urban Services.

They are also looking into Liu Hui, deputy general manager of Shenzhen Talents Housing Group, and Tang Yong, a former chairman at China Resources Land.

All four were "suspected of serious violations of discipline and law", the notices said, providing few details.

The language used in the announcements, however, typically indicates impending graft charges.

"This is a continuation of China's crackdown on corruption, from government agencies to financial institutions, and to state-owned enterprises," said Ting Meng, senior Asia credit strategist at ANZ Bank.

As sentiment in the sector is already weak, this news will "further suppress market confidence" and increase concerns about the internal governance of some state-owned firms, she told AFP.

The investigations come ahead of the ruling Communist Party's 20th National Congress, at which President Xi Jinping is widely expected to be anointed for an unprecedented third term.

Xi has championed an anti-corruption drive since coming to power, taking down big-name detractors, and observers expect him to use the months leading up to the meeting to cement his grip on power.

The probes follow a regulatory crackdown on some of China's biggest tech firms.

Authorities have also in recent months announced investigations into figures in the semiconductor industry, including minister for industry and information technology Xiao Yaqing.

Regulatory chiefs, insurance giants, security officials and financiers have faced censure or prosecution under the anti-corruption drive, but it is rare for a minister to be targeted while still in office.

The vast majority of people who have been investigated for corruption in China were eventually convicted.

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