Police officers in Huizhou, in South China's Guangdong province, check out the rubber slab used for counterfeiting 100-yuan banknotes, on Sept 24, 2015. [Photo/chinanews.com]

"The special operation was launched after nine months of investigation," Gao said.

"The large amount of high simulation fake money might have been in circulation if the underground production sites in Huizhou had been busted two to three days later, as production of most of the fake banknotes had been completed," he added.

Cen Daoai, vice-president of Guangzhou Branch of People's Bank of China, said Guangdong, one of the country's economic powerhouses, has been the main theatre in the fight against fake banknote production in the mainland for decades.

"Guangdong police has busted more than 60 fake banknote production sites since 2009," Cen said.

He urged banks and other financial organizations across Guangdong to continue to expand their co-operation with police in the fight against counterfeiting banknotes in the months ahead to curb the illegal operations.