China promised to stop harvesting executed prisoners' organs a year and a half ago, but a visiting investigator claims it is still killing as many as 100,000 people a year for body parts.
China had confirmed it used the organs of death-row prisoners but has long denied claims of the mass killing of minorities like Uighurs, Tibetans, Christians and Falun Gong adherents, too.
But United States human-rights investigator Ethan Gutmann says the sheer number of transplants, gathered from China's own records and sources, reveals the truth.
"This new evidence we have is actually quite explosive," Mr Gutmann tells SBS about his investigation with human rights lawyer David Matas and human rights activist David Kilgour into the number of transplants occurring in hospitals per year.
He says his team calculated 100,000 "without breaking a sweat", contrasting Chinese official figures of 10,000.
"We found this astounding and shocking."
He has testified to the US Congress.
It passed a motion of concern six weeks ago about "persistent and credible reports of systematic, state-sanctioned organ harvesting from non-consenting prisoners of conscience."
The Chinese Embassy did not reply to SBS's invitation to respond to the claims.
Mr Gutmann is visiting Sydney for the launch of the documentary Hard To Believe in which he features.