China executed more people in 2016 than all other nations combined, Amnesty International said Tuesday, even as death penalties in the world decreased overall.
The human rights organisation estimates the Asian giant alone killed "thousands" of people, a figure based on examinations of court records and news reports.
All other countries together executed at least 1,032 people last year -- a decline of 37 percent compared to 2015. Of those, 87 percent took place in just four countries – Iran, Saudi Arabia, Iraq and Pakistan.
Amnesty's report found that hundreds of death sentences, including cases involving foreign nationals, had been omitted from China's public database of court verdicts, suggesting a concerted effort to hide the extent of the country's killings.
The ruling Communist Party considers the death toll a state secret.
"China is really the only country that has such a complete regime of secrecy over executions," Amnesty's East Asia director Nicholas Bequelin said at a press conference in Hong Kong.
"Probably the reason is the numbers are shockingly high, and China doesn't want to be a complete outlier in the world," he said.
Despite local media reports saying at least 931 individuals were executed between 2014 and 2016, only 85 of them were in the online database, Amnesty said.
In 2013, China's Supreme People's Court ruled that legal judgements should be made public, but the decision included many exceptions, including cases involving "state secrets" or personal privacy.
Previous estimates from other rights groups also put the number of annual executions in China in the thousands.
Chinese courts have a conviction rate of 99.92 percent, and concerns over wrongful verdicts are fuelled by police reliance on forced confessions and the lack of effective defence in criminal trials.
The nation's top judge, Zhou Qiang, apologised in 2015 for past miscarriages of justice and said mistakes must be corrected.
In December 2016, a Chinese court cleared a man executed 21 years ago for murder, citing insufficient evidence in the original trial.
However experts say recent reforms have not been widely implemented.
"For example, coerced confessions are supposed to be excluded from evidence. In practise, however, the police have unchallenged discretion to...extract confessions by detaining and torturing suspects for long periods," New York University professor Jerome Cohen told AFP.
"Yet even the late Communist Party Chairman Mao Zedong, perhaps the greatest executioner in human history, recognised the likelihood of mistakes when imposing the death penalty," Cohen noted.
"Mao admonished his officials to bear in mind that, once someone’s head is cut off, it cannot grow back."
A 2016 report from the US-based Dui Hua Foundation said China's average death row prisoner waits only two months for execution.
Only a handful of countries still use the death penalty with regularity.
The United States executed 20 last year, the lowest figure for the country since 1991.