The gangsters obtained war weapons - guns, grenades and ammuniition - in Thailand and then smuggled most of them to China, according to police.
New national police chief Pol Gen Watcharapol Prasarnrajkit announced details of the operation at a press conference at the Royal Thai Police Office in Bangkok on Tuesday.
He said the Chinese embassy had asked Thai police to act against illegal trading in war weapons over the internet.
Police subsequently arrested two suspects, Chinese twins Yi Po and Yi Thao,.
Their accounts led police to the discovery of a large number of weapons dumped at Ban Suan-Setthakit 30 Road in Nong Prue sub-district of Muang Chon Buri district in Chon Buri province, and the arrest of three accomplices identified as Huang Suekerng, Seksan Satthai, 42, and Sakol Chairos, 32.
In addition to smuggling war weapons from Thailand to buyers in China, the gang also sold weapons to local people in Thailand, including teenagers in the eastern region, Pol Gen Watcharapol said.
"The transnational and online arms trade is growing," the acting police chief said.
Police found four pistols, three rifles, six 40mm grenades, and over 11,000 bullets dumped on Ban Suan-Setthakit 30 Road. Three suspects were arrested subsequently and police seized another eight pistols and 100 rounds of ammunition.
Pol Maj Gen Sanit Mahathaworn, acting commissioner of the Provincial Police Region 2, said the Chinese gang had been operating in Thailand for slightly over a year. Thai accomplices were told to collect firearms to meet orders placed online. Most of the firearms were registered, but their buyers were not.
He said Chinese were not the only foreigners working in the transnational arms trade in Thailand.
Chinese authorities would investigate where the weapons were sent to in China. Each weapons order placed with the gang was in "six figures", Pol Maj Gen Sanit said.
He said the gang and the weapons seizures had nothing to do with the recent political unrest in Thailand.
Pol Lt Gen Sakda Chuenpakdi, acting Immigration Bureau chief, said earlier four other accomplices had been arrested in China. The gang had smuggled weapons by hiding them in false compartments inside loudspeakers in vehicles sent from Thailand to China.