Rosangela Almeida dos Santos, 37, is said to have desperately tried smash her way out of the wooden coffin which had been nailed shut and could be heard screaming and groaning by neighbours.
Neighbours also heard bangs coming from the grave and but she had already died by the time it was finally opened.
But Ms Santos was "still warm" when she was examined and her hands and forehead were all bloody from where she had tried to claw her way out, according to local reports.
Some of the nails in the coffin had been pushed up too.
A video has since emerged showing the commotion in the Senhora Santana cemetery in Riachao das Neves, northeast Brazil, as local men took out the heavy coffin and removed the lid.
Married Mrs Santos was declared dead by a hospital on January 28 and was buried the next day.
People living near to the cemetery alerted her family on February 9 – some 11 days after she had been laid to rest – after hearing screams and bangs coming from inside the tomb.
Ms Santos had been at the Hospital do Oeste in Barreiras, in Brazil's northeastern state of Bahia, for a week after being rushed there by her family who claimed she was suffering from severe fatigue.
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She had two heart attacks before dying from "septic shock", according to her death certificate.
The woman, who was married but didn't have children, reportedly suffered fainting spells since she was seven-years-old and took anticonvulsant medicines.
Her family said their goodbyes at a wake held that night, and she was buried in a concrete tomb at the municipal cemetery in her home town, Riachao das Neves, the following day.
But last Friday residents living on the street next to the cemetery raised the alarm after hearing screams, banging and groans coming from inside the woman's stone tomb.
Housewife Natalina Silva told Brazil's G1 website that many people had heard muffled screams during the night.
She said: "When I got there right in front of the tomb, I heard banging from inside it.
"I thought the kids who play around the cemetery were playing a joke on me. Then I heard her groan twice, and after those two groans she stopped."
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Ms Santos' mother, Germana de Almeida, 66, said that when they took out and opened the coffin they found injuries to her body when she claimed weren't there when they buried her
She said: "She had tried to open the lid, even the nails that had been hammered in were loose. Her hands were injured, like she had been trying to get out."
Ana Francisco Dias, who lives near the cemetery, told Brazil's Globo TV station: "There were than 500 people who came here and packed the cemetery, everybody went to see, lots of people touched her foot and everybody saw that she was still warm. She wasn't cold."
The family believes that Ms Santos was declared dead in error have reported the incident to police.
Police chief Arnaldo Monte, who is leading the investigation, said: "We have today started to take statements from family members and other people.
"If need be, we will exhume Ms Santos' body again so we can get to the bottom of what really happened."
A spokesman for the Hospital de Oeste which declared her dead said they "will provide all necessary information requested from them to the family and authorities".