Authorities in Beijing are sweeping up all the “dirty cash” around the country.

Last week, Chinese police arrested 450 people who they believe have been illegally transferring money out of the country. According to state news outlets, the Ministry of Public Security (MPS), the People’s Bank of China and the State Administration of Foreign Exchange discovered a total of 192 locations where illegal banking services involving an estimated US$30 billion were provided.

Analysts at Goldman Sachs estimate that up to US$28 billion exited China last December, according to a Bloomberg report.

MPS officials said underground banks in the country have become channels for transferring money that been obtained through illegal activities, such as public funds embezzled by corrupted officials. The crackdown focused on “cross-regional and cross-border underground banks,” the ministry said.