BEIJING -  China executed more people last year than the rest of the world combined, Amnesty said Tuesday, defying a global decline with thousands of killings that have disproportionately targeted poor citizens.

Even as executions have dropped by more than a third globally, China's death penalty rate is "shockingly high" although the full extent of the secretive practice is unknown, Amnesty International said.

While President Xi Jinping's much-hyped corruption crackdown has seen many high-ranking figures sent to jail, their death sentences have often been commuted.

Meanwhile ordinary people caught in the crosshairs of the law have not been so lucky, it said.

Farmers were more frequently sentenced to death than any other group in China, Amnesty said in a report that sought to lift the veil on the workings of the system.

China's ruling Communist Party regards execution figures as a state secret, meaning that hundreds of death sentences are omitted from the public database of court verdicts.

"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. Although local media reports estimated that at least 931 individuals were executed between 2014 and 2016, only 85 of them were found in the online database, Amnesty said.

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. The nation's top judge, Zhou Qiang, apologised in 2015 for past miscarriages of justice, saying: "We feel deep remorse for wrongful convictions".

Only a handful of countries still use the death penalty with regularity. The United States executed 20 people last year, the lowest figure for the country since 1991. 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.