SHANGHAI (AFP) - Missing Chinese billionaire Xiao Jianhua's company said on Thursday (Feb 2) all was "normal" in his business empire but did not address reports that he was whisked to China for investigations into 2015 stock market turmoil.

Xiao went missing last week from Hong Kong and overseas Chinese-language media reports said he had been abducted by mainland security agents.

The case has sparked new fears that the semi-autonomous city's freedoms are under threat from Beijing.

"Production and operations of Tomorrow Holdings Ltd and its related companies are all normal," the company said in a brief statement on its WeChat account.

It expressed "thanks for the concern and kindness expressed by all friends in society toward Mr Xiao Jianhua and the company".

Hong Kong media say Xiao, a financier who has obtained Canadian citizenship, was last seen at his apartment in the city's harbourfront Four Seasons hotel.

The reason for the company announcement late Thursday was not clear, but Friday morning will see trading resume on China's stock exchanges after a week-long holiday break, including shares of companies said to be linked to the Beijing-based Tomorrow.

Three previous statements purportedly from Xiao denying he has been kidnapped have appeared.

Hong Kong's South China Morning Post said Xiao is in mainland China "assisting investigations" into the 2015 stock rout.

The Shanghai stock index tumbled nearly 40 per cent over a period of little more than two months.

Authorities helped inflate the bubble by encouraging investment. But when it burst, officials have sought to pin blame on market manipulators.

It is unclear how Xiao is being linked to the crash, but mainland investigators have targeted several investment executives on suspicion of insider trading since 2015.