Police officers in Huizhou in South China's Guangdong province examine the paper used for counterfeiting 100-yuan banknotes on September 24, 2015. [Photo/chinanews.com]

Workers were busy testing and mixing printing inks while two production lines were running at full speed.

They were equipped with walkie-talkie but were caught unaware when police suddenly broke in.

This is what police officers saw when they raided a major secret counterfeiting banknote site hidden in a metal and plastic factory in Boluo county of Huizhou in eastern part of Guangdong province on early morning of Sept 17.

The small workshop, which was installed with sound insulating equipment, stretched over 60 square meters. A small door about 130 centimeters high and less than 1 meter wide was found behind filing cabinets in an office of the factory.

Huang Shouying, director of economic crime investigation bureau under Guangdong provincial department of public security, recalled busting the biggest fake banknote production case in the Chinese mainland since 1949 on Thursday.

Police seized fake banknotes with a total face value of more than 210 million yuan ($33.07 million) after raiding two production bases in Huizhou and in other five Guangdong cities and Sichuan province on Sept 17, Huang told a press conference on Thursday.

A total of 29 suspects, including the gang leaders, have been detained and four printing machines, many films and related equipment and semi-finished products have been seized after the raids on the two counterfeiting bases in Huizhou.

He said the crackdown has dealt a heavy blow to the banknote counterfeiting operation in Guangdong province which borders Hong Kong and Macao special administrative regions.

Gao Weidong, deputy director of Huizhou city bureau of public security bureau, said more than 400 police officers took part in the special operation in Huizhou on Sept 17.

And one officer was injured during the raid.