BEIJING • China's central bank said all cryptocurrency-related transactions are illegal and must be banned, sending the strongest signal yet on its determination to crack down on the industry.

All cryptocurrencies, including Bitcoin and Tether, are not fiat currency and cannot be circulated on the market, the People's Bank of China (PBOC) said on its website.

All crypto-related transactions, including services provided by offshore exchanges to domestic residents, are illicit financial activities, the PBOC said in the statement.

This latest harsh directive, which sent Bitcoin dropping as much as 5.5 per cent yesterday, comes as global markets become increasingly concerned over a debt crisis involving property developer China Evergrande Group.

The Chinese government may also be responding to signs that miners are disguising their activities to stay in business.

Mr Vijay Ayyar, head of the Asia-Pacific with cryptocurrency exchange Luno in Singapore, said that while the Chinese government has made similar statements in the past, it is "a slightly nervous environment for cryptocurrencies with the recent SEC (Securities and Exchange Commission) comments and overall macro environment with the Evergrande news. So any comments of this nature will cause a sell-off in risky assets".

The nation's economic planning agency also said it is an urgent task for China to root out crypto mining, and the crackdown is important to meet carbon goals.

Investors should expect "knee-jerk price reaction as China takes the wind out of Bitcoin's sails", said Mr Antoni Trenchev, co-founder of crypto lender Nexo. "The recent rebound from just below US$40,000 has likely run its course for now."

Argo Blockchain slumped 10 per cent in London, while Bitcoin miner Northern Data AG lost 2 per cent in Frankfurt.

In US pre-market trading, MicroStrategy, the enterprise software company that has more than US$5 billion of crypto assets, lost 3.5 per cent.

Riot Blockchain and Bit Digital each fell about 5 per cent.

BLOOMBERG