In this photo illustration, the Bitcoin logo is seen on a mobile device with People’s Republic of China flag in the background. (Photo Illustration by t/SOPA Images/LightRocket via Getty Images)Budrul Chukrut | SOPA Images | LightRocket | Getty ImagesGUANGZHOU, China — Huobi, one of the world’s largest cryptocurrency exchanges, said it has ceased new account openings for mainland Chinese users after Beijing renewed a crackdown on virtual currencies.The People’s Bank of China declared all virtual currency-related activities illegal including trading on Friday. The Chinese central bank also took aim at overseas exchanges providing services to mainland China users.Huobi, one of these exchanges, said on Sunday that it would end account registrations for new mainland Chinese users. The company will also gradually retire existing accounts of mainland Chinese users by midnight on Dec. 31, 2021. Meanwhile Binance, one of the world’s largest cryptocurrency exchanges, said that account registrations using Chinese mobile phone numbers are now blocked. The Binance app is also no longer available for download in China.”Binance takes its compliance obligations very seriously and is committed to following local regulator requirements wherever we operate,” a spokesperson told CNBC.This year, Chinese authorities have intensified a crackdown on cryptocurrencies that has targeted bitcoin miners and trading.But China’s tough stance on cryptocurrencies is not new. Authorities in the world’s second-largest economy have long been worried about the impact of digital coins on financial stability.In 2017, China shut down local cryptocurrency exchanges and banned so-called initial coin offerings (ICOs), a way to raise money for crypto companies by issuing digital tokens. Many of China’s cryptocurrency exchanges moved offshore as a result of that. But loopholes have remained that allow mainland Chinese traders to buy and sell digital currencies on these offshore exchanges.