A "serious adverse" incident in the Brazilian trial of the Chinese developed Covid-19 vaccine has resulted the programme being halted.
The health authorities reported the incident took place on October 29 but provided no specific details.
The team running the trial say a person involved had died but the death is unrelated to the ongoing study.
The CoronaVac vaccine, created by the Chinese firm Sinovac Biotech, was in the final stages of testing but this has now been delayed.
Sinovac, however, say they are "confident in the safety of the vaccine" and trials are continuing in other countries.
Brazil has suffered badly from coronavirus, with 163,000 deaths reported in the country.
Brazilian health regulator Anvisa say they "ruled to interrupt the clinical trial of the CoronaVac vaccine after a serious adverse incident".
The head of Butantan, the medical research institute conducting the Brazilian trial, says a death was the reason they were required to stop.
"We learned the head of Butantan Institute believed that this serious adverse event (SAE) is not related to the vaccine," Sinovac said in a statement.
"The clinical study in Brazil is strictly carried out in accordance with GCP (Good Clinical Practice) requirements and we are confident in the safety of the vaccine."
Brazil's President Jair Bolsonaro has previously stated his preference for a vaccine made by AstraZeneca, stating his government would not purchase one from China.