President Jair Bolsonaro stepped up criticism of the vaccine last month, saying China lacks credibility to come up with solutions for the coronavirus crisis and that people wouldn't feel safe with the shot "due to its origin".
Brazil has stopped trials of Chinese vaccine "Corovac" after one of its volunteers suffered "serious adverse effects".
The report comes even as American company Pfizer was upbeat after its Covid-19 vaccine candidate showed 90 per cent efficacy in late-stage trials, according to an interim analysis.
Sinovac said in a statement: "The clinical study in Brazil is strictly carried out in accordance with GCP requirements and we are confident in the safety of the vaccine".
Brazil's health regulator, Anvisa, said late on Monday that the event occurred on October 29 but did not specify if it took place in Brazil or in another country.
Halts to investigate serious adverse events are not uncommon in large-scale drug trials and two western developers - AstraZeneca Plc and Johnson & Johnson - have paused their vaccine trials in recent months due to such incidents, only to re-start them after investigation.
"There is no relation with the vaccine", said Dimas Covas, head of the Butantan Institute, the respected public health center coordinating the study in Brazil. Brazil's health authority, Anvisa, did not indicate when or if the trials would resume.
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CoronaVac has been caught up in a messy political battle in Brazil, where its most visible backer has been Sao Paulo Governor Joao Doria, a top opponent of far-right President Jair Bolsonaro.
Sinovac is also hoping to supply its experimental coronavirus vaccine to more South American countries by outsourcing some manufacturing procedures to Butantan. He sparked confusion last month when he publicly rejected it, saying Brazilians would not be used as guinea pigs.
Earlier on Monday, Sao Paulo state's health secretary, Jean Gorinchteyn, said the first 120,000 CoronaVac jabs would arrive at Sao Paulo's worldwide airport November 20.
Sao Paulo state has a deal with Sinovac to buy a total of 46 million doses - six million produced in China and the rest produced in Sao Paulo, which broke ground last week on a factory to make the vaccine domestically.
Anvisa told AFP it had no comment beyond its statement announcing the suspension, which said that halting trials was standard procedure in such cases. The trial, which involved China's Sinovac vaccine candidate, named CoronaVac, had seen a death, but the fatality that occurred was unrelated to the vaccine, Reuters reported.
And both are being tested in Brazil, the country with the second-highest death toll in the pandemic, after the United States, with more than 162,000 people killed by the new coronavirus.