By Donny Kwok

HONG KONG (Reuters) - Online game developer Boyaa Interactive International Ltd said its chairman is being investigated by judicial authorities in China, although details of the probe were not yet known - sending its shares sliding 20 percent to a record low.

Chairman Zhang Wei, who is also a controlling shareholder of the company, had been detained, Hong Kong-listed Boyaa said in a statement late on Wednesday, adding that business operations remained normal.

"The company has not received any notice of an investigation or a request to assist in any investigation," Boyaa said in the statement. "No action has been taken or threatened to be taken by any authorities to freeze any of the assets of the company."

It gave no further details.

The shares fell as low as HK$2.23, their lowest level since the firm's listing in November 2013. They were last trading down 16.5 percent, giving the firm a market value of $233 million.

(Reporting by Donny Kwok; Editing by Anne Marie Roantree and Edwina Gibbs)