A South Florida woman has been charged over the death of her baby son found dead in a freezer at her home.

Paola Vargas-Ortiz, 37, has spent the past month in a mental health care centre, but Miami-Dade police took her into custody on Thursday and charged her with manslaughter, the Miami Herald said.

Authorities say Vargas-Ortiz was poised to jump from the Seven Mile Bridge in the Dlorida Keys on January 17 when she told them she had thrown her four-month-old son Hugo in first.

But after Monroe County deputies took Vargas-Ortiz into custody, she told them the child was actually dead in a freezer. Police went to the woman's home in Homestead and found the child's body.