The coronavirus vaccine, developed by private Chinese pharmaceutical firm Sinovac, is the third in the world to enter Phase 3 trials, or large-scale testing on humans -- the last step before regulatory approval.
It will be administered to doctors and other health workers who volunteer for the program across six states in Brazil, one of the countries hit hardest by the pandemic.
"Trials of CoronaVac, one of the vaccines that has advanced furthest in testing in the world, will begin at the Clinical Hospital of Sao Paulo," the state's governor, Joao Doria, told a news conference.
He said initial results were expected within 90 days.
Sinovac is partnering with a Brazilian public health research center, the Butantan Institute, on the trials.
If the vaccine proves safe and effective, the institute will have the right to produce 120 million doses under the deal, according to officials.
"In Brazil, we could have the first vaccine to be put to widespread use, which is very, very promising," said the head of the Butantan Institute, Dimas Covas.