Beijing has forced nearly 10,000 Chinese overseas nationals to return since 2014 using coercive means outside the justice system, according to a new report.

The figure could be the "tip of the iceberg", Spain-based rights group Safeguard Defenders reported Tuesday, as China aggressively pursues its nationals overseas.

The report alleges China is expanding its policing powers overseas and conducting illegal operations on foreign soil.

Officially, the targets are people wanted by the Chinese judicial system as part of President Xi Jinping's anti-corruption drive.

But the NGO details cases where those who criticised the Communist Party had relatives in China harassed and detained in attempts to coerce them to return.

Through two programmes, Operation Fox Hunt and Operation Sky Net, targeted individuals were pressured to return to China against their will due to a combination of non-judicial methods, including kidnappings, harassment and intimidation, according to the report.

"With the Chinese diaspora growing at an ever faster rate as more people seek to leave China... Beijing has never been more motivated to expand the powers of its security forces overseas," the report said.

Safeguard Defenders cited government data in its estimate that almost 10,000 Chinese nationals had been forcibly returned since 2014.

China
This is a representational image. AFP / NICOLAS ASFOURI

Official figures from the government's anti-graft watchdog show Beijing returned around 2,500 targeted individuals in the past two years.

But the numbers do not include suspects apprehended for non-economic crimes or those who are not members of China's ruling Communist Party.

The NGO's report alleges intimidation of suspects' family members in China is widespread and Chinese agents are sent to threaten targets in foreign countries.

Sometimes overseas nationals are lured to third countries that have extradition agreements with China, the rights group says.

Operation Fox Hunt was launched in 2014 to track down expatriates wanted for economic crimes while the larger Operation Sky Net kicked off in 2015 and was later folded into Fox Hunt.

China has previously been accused of carrying out kidnappings abroad.

In 2015, bookseller and Swedish citizen Gui Minhai was allegedly abducted from Thailand before later reappearing in Chinese custody.

Two years later, billionaire businessman Xiao Jianhua disappeared from a Hong Kong hotel and is believed to be still in custody in China.

In China, the Communist Party-controlled courts convict most people who stand trial.