Update: Confirming the other speculation, that China would halt all cryptocurrency exchange, Yicai reports that it is not just BTC China: 

CHINA MAY SHUT ALL LOCAL BITCOIN EXCHANGES BY SEPT. END: YICAI

To which the response from the Bitcoin Association of Hong Kong is: "if China restricts growth in bitcoin" it will drive business to us"

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Yuan-denominated Bitcoin has crashed as much as 25% 35% in Chinese trading, plunging from 25,000 yuan to as a low of 16,000 on local exchanges BTCChina (and as low as 20,000 on OKCoin), following confirmation of last week's Caixin report that Beijing would stop cryptocurrency exchange trading. China's second largest exchange, BTC China, said that it would halt all trading on the platform beginning September 30, launching a liquidation panic.

In a statement released on Weibo, BTC China said that it would immediately stops accepting new account registrations on BTCChina Exchange. The decision was made after "carefully considering" Chinese regulatory bodies' Sept. 4 announcement on preventing risks associated with token fundraising. A google-translated version of the statement:

China will stop all trading business on September 30th

Dear Bitcoal Chinese users: According to the September 4 issue of the "People's Bank of China Central Office of the Ministry of Industry and Information Technology Ministry of Industry and Commerce, China Banking Regulatory Commission, China Securities Regulatory Commission on the prevention and treatment of the risk of the issuance of the currency," the spirit of the document, adhering to the protection of investment risks, the maximum protection of users

The principle of interest, Bit Coin Chinese team by careful discussion, is to make the following decision:

1. Bit currency China's digital asset trading platform today to stop the registration of new users;

2. September 30, 2017 Digital asset trading platform will stop all trading business.

Beitou China's pool (pool) and other business will not be affected, continue to normal operation.

We apologize for the inconvenience. If you have any questions, please contact support@btcchina.com.