Regulators have ordered Chinese bitcoin exchanges to close, two business newspapers reported Thursday, after uncertainty about the digital currency's future in China caused its price to plunge.

Regulators in Shanghai, the country's financial center, gave verbal instructions to exchange operators to shut down, China Business News and 21st Century Economic Report said on their websites. They gave no other details.

The central bank has yet to respond to questions about bitcoin's future in China but earlier warned it was traded without regulatory oversight and might be linked to fraud. The bank banned initial offerings of new digital currencies last week.

Bitcoin is created and exchanged without the involvement of banks or governments. Transactions allow anonymity, which has made bitcoin popular with people who want to conceal their activity. Bitcoin can be converted to cash when deposited into accounts at prices set in online trading.

Rumors that China planned to ban bitcoin has caused its market price to tumble 20 percent since Sept. 8.

Interest in China in bitcoin surged last year after the price rose. A Chinese business news magazine, Caixin, said at one point up to 90 percent of global trading took place in China.

Trading volume has fallen as regulators tightened controls.

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