In its annual global review of executions released on Monday, the rights group said it found media reports of 305 executions carried out in China a year ago, but only 26 cases were in the court database.
Globally, Amnesty counted 1,032 executions worldwide in 2016 - excluding China - down from a spike in executions in 2015.
Amnesty's China-focused report, China's Deadly Secret, said for 2016, the group found 305 executions using a Chinese search engine, but only 26 of those cases made it to a national database.
China is believed to have executed "thousands" of people, more than the combined figure of at least 1,023 executions in 23 other countries past year, the rights group said.
Whilst China has been taking steps towards reforming its death penalty policies, it is hard to assess the progress without more transparency, William Nee, the lead author of the report told HKFP.
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"The Chinese government is claiming that it is bringing transparency to the judiciary and judicial verdicts".
"This shows that judges and juries are less inclined to resort to this flawed and cruel practice", said James Lynch, deputy director of Amnesty International's Global Issues Programme. The report from Viet Nam's Ministry of Public Security does not contain a breakdown of figures for 2016.
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.
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The number of executions (20) in 2016 reached the lowest level recorded in any year since 1991, half what it was in 1996, and nearly five times lower than in 1999.
For the first time in a decade the U.S. was not one of the five biggest executioners, giving hope to human rights activists. The overall number of executions carried out in Iran, however, dropped by 42% (from at least 977 to at least 567) compared to the previous year.
Amnesty said the decrease in executions was due partly to litigation on lethal injection protocols and challenges in sourcing chemicals in several states.
The authors also note that drug-related offences do not belong to the category of "most serious offences" to which the death penalty should be restricted under global law. However, 2,832 people were still on death row in the United States of America at the end of 2016.
However, Susan Trevaskes of Australia's Griffith University, concluded in a recent study that close to half of all death sentences were handed down for drug crimes. The number of executions was higher again than people had expected.
Only five USA states executed people in 2016: Alabama (2), Florida (1), Georgia (9), Missouri (1), Texas (7), with Texas and Georgia, accounting for 80% of the country's executions in 2016.
The report assumes significance as it shows India is not moving away from the death penalty, as was strongly recommended by the law commission in 2015. "The shocking number of executions scheduled over a ten-day period in Arkansas this April is a clear example of how quickly the picture can change", said Salil Shetty. The concern with China is that capital punishment is used as a political tool.
"If governments in Beijing, Manama, Islamabad and Riyadh see there's very little public outrage over executions, then they're going to think they've got a green light to carry on killing". The fact that "there are so many farmers and migrant workers being sentenced to death would probably indicate that, as in line with the experience of other countries, relatively poorer people are more likely to be subjected to the death penalty, or are perhaps less able to afford adequate and effective legal representation", said Nee.