WATCH - Video of Black man asphyxiated in car trunk by Brazil Police sparks outrage

The death of a Black man has sparked widespread outrage in Brazil after videos showed police officers holding him in the trunk of a smoke-filled police vehicle while attempting to arrest him.

Viral images from a police stop in Umbauba, in Brazil's northeastern state of Sergipe, show the officers forcing 38-year-old Genivaldo de Jesus Santos in the back of their police vehicle, with smoke pouring out of the trunk.

They lean down on the trunk door to prevent Santos from leaving, even as a cloud of white smoke emerges from the car.

On Thursday, an autopsy by the state forensic medical institute found that Santos died from "mechanical asphyxia," the Associated Press reported.

Brazil's federal police said they had opened an investigation into the circumstances of the death.

Mass protests call for justice

Emerging days after another case involving police violence, the shocking images sparked horror across social media, leading to protests in the town of Umbauba on Wednesday. Demonstrators closed the highway and set tires on fire, waving signs demanding justice.

"The population is outraged," a protester said according to news agency AFP, while another addressed the crowd saying, "They murdered the guy!"

Santos' family said he became nervous when the officers found his prescribed schizophrenia medicine in his pocket. Wallyson de Jesus, a nephew of Santos', was present at the time of his uncle's detention.

"They threw some kind of gas inside the trunk and went to the police station, but my uncle was unconscious. They took him to the hospital, but it was already too late," he told local media.

The Federal Highway Police's statement said the man was "actively resisting" the officers when pulled over, causing the agents to immobilize him. The statement said the officers used "instruments of lesser offensive potential" to contain him.

It added that he fell ill while he was being transported to a police precinct, and was taken to a hospital, where his death was confirmed.

Repeated instances of police violence

The shocking incident came to light days after officers of the highway police in Rio de Janeiro took part in an operation that left more than 20 people dead. While the police said they were forced to use lethal force, residents have countered the claims.

President Jair Bolsonaro mentioned a separate case from two weeks ago where a man shot two on-duty highway officers and said he would find further details about the latest incident from the Federal Highway Police.

The latest incident "shocked Brazilian society due to the level of its brutality, exposing the institution's lack of preparedness to guarantee that its agents obey basic procedures," the Brazilian Public Security Forum, an independent group, said in a statement.

"This was a crime, perpetrated with cruelty," Santos's wife Maria told local news network G1.