Beijing police have raided more than 10 underground banks that were involved in $23 billion (€18.47 billion) worth of transactions as authorities tighten their controls on the movement of money across China’s borders.

The raids took place on September 18th and the police made 59 arrests.

China’s relationship with the underground banking sector is complicated. Earlier this year, the government made a new rule to legalise underground lending, following a government decision in 2012 giving private firms in Wenzhou permission to set up lending businesses to try to stem underground banks, which were charging high interest rates to borrowers.

China, which limits the movement of capital as part of controls on the value of its currency, has tightened checks on the flow of cash to crack down on money laundering and close loopholes used to evade regulations.

In September, the forex regulator said it uncovered €8 billion in fraudulent trade.