China’s war on underground banking is having great success, particularly in the province closest to the world’s top gambling hub, Macau.

According to the Guangdong provincial Department of Public Security, police in China’s most populous province cracked 83 cases involving underground banking transactions between April and December 2015, seven times the number of cases than police recorded in all of 2014.

Huang Shouying, director of the Department’s economic crime investigation bureau, told China Daily that police had exposed 79 illegal banking sites, detained 231 suspects, seized RMB 37.1m (US $5.6m) in cash and froze 3,491 accounts containing RMB 665m ($101m).

Shouying said underground banks were channels for “online gambling, telephone fraud, moving suspected drug trafficker’s money in and out of the mainland and domestic corrupt officials sending their bribes abroad.” That last category includes a pair of officials from Jiangxi province who used a Guangdong underground bank to send RMB 12.8m to an account in Macau last June.