Police in Anqiu, Shandong province, have made dozens of arrests in action against a company illegally producing guns, China Central TV reported on Sunday.

Officers were alerted by a package sent by a man, surnamed Zheng, that was found to contain gun parts in October last year.

"After investigation, we found Zheng would disassemble the guns and send the parts in separate packages mixed with hardware and metals," Yang Guoxiu, a police officer from Anqiu, told CCTV news.

Since 2016, police said Zheng's factory had been producing a kind of toy called a "match gun", which could be modified into a real gun, and selling them online.

Zheng admitted to hiring workers to design and produce match guns from a drawing he downloaded from the internet. He sold more than 1,000 online for 688 to 1,397 yuan ($100 to $210) each, netting a profit of over 1 million yuan.

Yang said holding more than 30 gun parts constitutes a crime under Chinese law. 

Police officer Cao Guoping told CCTV news the investigation had found some of Zheng's customers were buying used gun shells online before filling them with fresh gunpowder for second use.

So far, police on the case said they have detained 57 people and seized 43 guns, along with some 4 metric tons of ammunition.