Chinese police have busted underground banks that handled 200 billion yuan ($30.2 billion) in illegal money transfers this year, the Ministry of Public Security said on Wednesday.

Police said they arrested 450 suspects involved in 158 cases of underground banking and money laundering, according to the ministry's website.

Beijing has been fighting illegal cross-border outflows in an attempt to slow capital flight as the yuan currency weakened to near six-year lows.