Seven people have been detained in an operation to break up two underground banks worth more than 20 billion yuan ($3.08 billion) in Guangdong province.

Shaoguan city police said on Thursday more than 10,000 people are suspected to have used the illicit operations to transfer money in or out of the country or exchange currencies.

Some of the money was sent to Macao to fund gambling activities, the police said.

The banks' operators are also believed to have earned large profits from illegal foreign currency settlements using 48 bank accounts opened using fake documents in more than 20 provincial regions.