Image caption The suspects will now face trial in China

Angola has extradited 37 Chinese nationals, accused of extortion, kidnappings, armed robberies and running prostitution rings.

They allegedly targeted other Chinese, kidnapping businessmen for ransom and sometimes burying victims alive.

They lured women to Angola, promising well-paid jobs, but then forced them into prostitution, Chinese police said.

Tens of thousands of Chinese live in Angola, and Chinese state-run firms have large interests in the country.

China's Ministry of Public Security said a special police team was sent to Angola in July to help investigate criminal gangs.

The ministry said the officers had helped their Angolan counterparts break up 12 gangs and free 14 victims, most of whom were thought to be women forced to work as prostitutes.

The 37 suspects arrived at Beijing airport in handcuffs with balaclavas covering their faces. They are due to be tried in China.

Mineral-rich Angola is China's biggest trading partner in Africa, with some $24.8bn (£15.7bn) in 2010.

Commercial opportunities have attracted private businesses and state-run firms.

But according to Chinese media, crime had begun to seriously affect operations in the country.

China Police, a website run by the ministry, published an article documenting 14 kidnappings during 2011 in which five victims were killed.

The article said Chinese business owners had moved away from the capital Luanda, while others had hired private security guards and bought bullet-proof cars.