China's central bank has ordered the country's commercial banks and payment companies to close bitcoin trading accounts in two weeks, according to people with knowledge of the matter, dealing another blow to the virtual currency.

Bitcoin prices are down roughly 8% since the new rules were first reported in financial publication Caixin last week. The rules affect more than a dozen bitcoin exchanges, and are a further tightening of regulations the central bank put in place last year. The accounts must be shut down by April 15, the people said.

Authorities have kept an eye on bitcoin's expansion here as it poses a potential threat to financial stability and because it has attracted swarms of speculative retail investors looking for ways to make quick profits. China imposes strict capital and currency controls, but bitcoin, in theory, offers its holders a way to bypass those rules. Chinese demand for bitcoin soared late last year, contributing to a rise in global prices and attracting the attention of regulators.

Regulators are also concerned about the safety of bitcoin exchanges following the collapse of Japan's Mt. Gox exchange after most of the bitcoins it was holding were stolen.

The latest move by the People's Bank of China is a huge blow to the country's bitcoin exchanges, which have found their footing in the more than three months since Chinese authorities appeared to take measures clamping down on the industry. In December, the PBOC ordered financial institutions to stop dealing with bitcoin. Later that month, it made clear that third-party payment processors could not help exchanges collect money from users.