Dozens of Chinese firms are producing and exporting "tools of torture", from electric stun guns to metal spiked batons, to countries with bad human rights records, rights group Amnesty International said on Tuesday.
More than 130 companies are involved in producing or trading the equipment, typically marketed to law enforcement agencies, up from about 28 companies a decade ago, Amnesty said.
The equipment fuels human rights abuses by law enforcement authorities in African and Southeast Asian states, the group said in a report.
"While some of the exports are no doubt used in legitimate law enforcement operations, China has also exported equipment that has inhumane effects, or poses a substantial risk of fuelling human rights violations by foreign law enforcement agencies," it said.
One company, China Xining Import/Export Corporation, which advertises thumb cuffs, restraint chairs and electric stun guns, said in 2012 it had ties to more than 40 African countries, according to Amnesty. The firm could not be reached for comment.
The rights group worked with the British-based Omega Research Foundation, which researches the trade and the use of military, security and police equipment.
China's Foreign Ministry could not be immediately reached for comment.
China is a major investor in resource-rich Africa and the government said in July more than half its foreign aid of more than $14 billion between 2010 and 2012 was directed to Africa.
Torture by law enforcement authorities is a pervasive problem within China. The country's top court said in November it would eliminate the use of torture to extract confessions.
Amnesty said news photographs from Ghana, Senegal, Egypt and Madagascar appear to show police toting Chinese-made electric shock stun batons.
"Amnesty International and Omega consider that some of the weapons and equipment manufactured in China have inherently abusive effects that are contrary to international human rights standards for law enforcement," the group said.