A government spokesman said, "The police are currently investigating Zhou's problems." He gave no further details on the "problems".

He said Zhou had been in custody since October.

Zhou was released from prison in May after completing a three-year sentence for "controlling securities prices and making a false report of registered capital".

Zhou, 45, who started business as a teenager in a wonton noodle shop and graduated to number 11 on Forbes' list of 100 richest mainlanders, was the majority shareholder of Hong Kong-listed Shanghai Land Holdings and Shanghai Merchants Holdings.

In 2002, Forbes estimated Zhou's wealth at about 320 million U.S. dollars.