China has prevented increasing numbers of people from leaving the country as part of efforts to tighten controls under President Xi Jinping, a human rights group said Tuesday.

Since 2018, Beijing has passed five new or amended laws expanding its ability to impose so-called exit bans, bringing the total to 15, according to Madrid-based rights group Safeguard Defenders.

"Since Xi Jinping took power in 2012, China has expanded the legal landscape for exit bans and increasingly used them, sometimes outside legal justification," the group said in a report.

Between 2016 and 2020, there was an eightfold-increase in the number of cases where exit bans were mentioned in the Chinese Supreme Court's legal database, the report said.

"Exit bans have become one of the many tools used by the Chinese Communist Party as part of broad efforts to tighten control over all aspects of people's lives," it added.

"Many are unaware of their exit ban until they are at the border attempting to leave the country."

Local laws governing the use of exit bans are "vague, ambiguous, complex and expansive", it said, noting they were often "impossible" to appeal.

While stressing that a lack of official data made specific figures hard to come by, the report estimated that tens of thousands of Chinese nationals were under exit bans at any one time.

The rights group said anecdotal evidence from "rights lawyers and human rights defenders in China" also suggested that "the problem of politically-targeted exit bans has been growing worse over the past five years."

It also said that dozens of foreigners had been prevented from leaving China in recent years.

Among those targeted have been lawyers, journalists and foreign business executives, the report said.

A study published last year cited by Safeguard Defenders also found that 128 foreigners -- including 29 Americans and 44 Canadians -- were slapped with exit bans between 1995 and 2019.

Foreign business lobbies have warned that changes to Beijing's counter-espionage law announced last week may increase the risk of people being given arbitrary exit bans.

"The additional scrutiny of firms providing essential business services dramatically increases the uncertainties and risks of doing business" in China, the American Chamber of Commerce said in a statement last week.

"This is a matter of serious concern for the investor community."