Saudi Arabia executed 184 people in 2019 — the most since records began in the ultraconservative kingdom — according to watchdog Amnesty International's annual report on the death penalty.

Key points: Saudi Arabia executed 37 people on a single day in 2019, including children

Saudi Arabia executed 37 people on a single day in 2019, including children Amnesty International estimates thousands of people are put to death in China each year

Amnesty International estimates thousands of people are put to death in China each year The Trump administration seeks to resume executing people after almost two decades

Most of those executed by the Saudi Government were convicted of violent crimes or drug offences, however Amnesty said Crown Prince Mohammed Bin Salman was increasingly using the punishment as a way to silence critics of his regime from the country's Shia Muslim minority.

"Saudi Arabia's growing use of the death penalty, including as a weapon against political dissidents, is an alarming development," said Clare Algar, the organisation's senior director for research.

Saudi Arabia reached its 800th execution since 2015 earlier this month, according to anti-death-penalty organisation Reprieve.

The NGO said in a statement that despite the Crown Prince's promise to "minimise" use of capital punishment, "this latest grim milestone shows that the opposite is in fact the case".

US President Donald Trump is an enthusiastic supporter of capital punishment. ( Reuters: Kevin Lamarque )

The kingdom beheaded 37 people for "terrorism" offences on one day in April last year, several of whom were minors.

"For all the rhetoric of reform and modernisation, Saudi Arabia is still a country where speaking out against the King can get you killed," Reprieve director Maya Foa said.

"In the run-up to the G20 summit in Riyadh in November, the kingdom's Western partners must demand an end to the execution of children and political opponents."

The Saudi embassy in Canberra did not respond to the ABC's request for comment.

Prior to lethal injection, those charged with the death penalty in the US are strapped into full-body chairs. ( AP: Eric Risberg )

China remains world's top executioner, Amnesty says

No countries abolished the death penalty during 2019.

"In countries from Belarus to Botswana and Iran to Japan, executions were being carried out without any advance notice to the families, lawyers or in some cases the individuals themselves," Ms Algar said.

While the Philippines abolished the death penalty in 2006, President Rodrigo Duterte has called for it to be reinstated for drug offenders.

Nevertheless, Amnesty reported the first drop in executions across the Asia Pacific since 2011.

Confirmed executions worldwide decreased by 5 per cent since 2018, it said, as strong proponents of the death penalty including Japan, Singapore and Egypt recorded "significant reductions" in the number of people they killed last year.

While data is not publicly available for China, Amnesty believes thousands of convicts were executed in 2019, making it by far the world's most prolific user of the death penalty.

The Communist governments of China, Vietnam and North Korea classify details of executions as "state secrets".

China's Supreme People's Court in late 2019 said the death penalty was "only administered for an extremely small number of convicted criminals of extremely severe offences".

Canadian national Robert Schellenberg was sentenced to death in China after appealing against his 15-year prison sentence for drug trafficking. ( CCTV )

Two Canadians were last year sentenced to death for drug offences in China, which Prime Minister Justin Trudeau slammed as "arbitrary".

Iran does not make its data public either, however Amnesty estimates it is the world's second-largest executioner, with more than 250 put to death in 2019.

Trump administration seeks to reinstate death penalty

US President Donald Trump, meanwhile, has long endorsed capital punishment, including for mass shooters and drug traffickers.

While the US Federal Government has not carried out an execution since 2003, the Trump administration attempted to reinstate use of the death penalty in mid-2019.

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A court in Washington earlier this month, rejected an appeal to block four capital punishment sentences from being carried out, providing a boost to Mr Trump's reinstatement of federal executions.

At the state level, 22 people were put to death in the United States during 2019.

But Amnesty praised the Government of California for putting a moratorium on executions, and New Hampshire for becoming the 21st US state to abolish the punishment.

"Our death penalty system has been, by all measures, a failure," California Governor Gavin Newsom said in March last year.

"It has discriminated against defendants who are mentally ill, black and brown, or can't afford expensive legal representation."

Donald Trump took out an advertisement advocating for the death penalty in a case known as 'The Central Park Five' in 1989. ( Supplied )

"The death penalty is an abhorrent and inhuman punishment, and there is no credible evidence that it deters crime more than prisons terms," Ms Algar said.

"We are calling on all states to abolish the death penalty. There needs to be international pressure on the world's last remaining executioners to end this inhuman practice for good."

Australia has not executed anyone in more than half a century, however capital punishment remained on the books in New South Wales until 1985.