The Hong Kong chief of a major Chinese brokerage who went missing last month has returned to work after "assisting" with an investigation on the mainland, the company said Wednesday.

The disappearance of Yim Fung, chairman of Guotai Junan International, came at a time when Beijing is targeting the financial sector in an anti-graft campaign.

In a statement to the Hong Kong stock exchange, the firm said that Yim would resume his duties Wednesday.

"Dr. Yim, in his personal capacity, had been assisting in certain investigations carried out by mainland authorities during the period he was unable to be reached," the statement said.

"Neither Dr. Yim himself nor the company was the subject of the investigations."

Last month Guotai International filed a statement to the Hong Kong exchange saying it had been unable to reach Yim.
The Hong Kong-listed firm is a subsidiary of Guotai Junan Securities, one of China's biggest security companies, and its shares plummeted on news of the disappearance.

On Wednesday the firm's stocks were up 6.9 percent in morning trade at HK$2.79 after news of Yim's reappearance.

Yim's month-long absence came as China zeroes in on the financial sector, as part of a sweeping anti-corruption campaign in the wake of a stock market rout that rocked global markets over the summer.

Chinese authorities have been pursuing crooked officials since President Xi Jinping took office in 2013, a crusade that some experts have called a political purge.

State media reported in November that Yao Gang, the deputy chief of China's top securities regulator, is under investigation for committing "severe disciplinary violations" -- normally a euphemism for graft.

In October, China's anti-corruption watchdog said it would expand its inspections to major financial institutions, which are already under pressure after a spectacular stock market meltdown.

After soaring 150 percent in one year, Shanghai stocks went into a tailspin in June, tumbling nearly 40 percent in a few weeks despite massive intervention by the authorities.