Shares in media company Camsing International crashed 90 percent in Hong Kong on Monday after it said its chairwoman had been arrested in China.
In a statement to the city's stock exchange, Camsing said the board became aware Friday that Lo Ching, who was also an executive director, was "currently being held in criminal custody" by the Yangpu Branch of the Shanghai Public Security Bureau.
"The directors are unable to ascertain the reasons of, or incidents leading to, the criminal custody of Ms Lo," it added.
The firm's stock collapsed as much as 90 percent Monday before pulling back to end 80.39 percent down at HK$0.90.
Lo is also chairwoman of Shanghai-listed Jiangsu Boxin Investing and Holding, which on Monday fell by the maximum 10 percent allowed.
Camsing in 2017 bought Pow! Entertainment, the company co-founded by Stan Lee, the late creator of superhero characters including Black Panther and Spider-Man.
News of Lo's arrest comes days after it emerged that Wang Zhenhua, the billionaire founder of property firm Future Land Development Holdings, had been taken into custody, sending the firm's share price tumbling 40 percent in three days.