A 23-year-old day care worker 'tortured and killed' a baby in her care.

A US day care worker has been captured on video “torturing” an eight-month-old girl who later died, authorities say.

Leah Walden, 23, is charged with murder, assault, child abuse and reckless endangerment in the death of Reese Bowman at Rocket Tiers Learning Centre on Tuesday, Baltimore Police said in a statement.

“Reese Bowman, in my opinion, was tortured,” said Colonel Stanley Brandford, the chief of the police department’s criminal investigations division.

Brandford said the video shows Walden using "excessive blankets, which fully covered the child's head, violently snatching the child out of the crib with one arm, swinging at the baby as if she was slapping her, and placing pillows over the baby's face." Walden also walked out camera range several times while holding the baby.

Police took Walden into custody early on Thursday.

Police said officers were called to the day care on Tuesday for a report of a baby not breathing. Medics performed CPR on the infant, who was taken to the University of Maryland Medical Centre and pronounced dead a short time later. Brandford said there were no obvious signs of trauma, but detectives started a routine investigation.

Brandford said Walden told them she fed the baby, wrapped her in a blanket and put her down for a nap. The management of Rocket Tiers alerted police to the video, which told a different story, Brandford said.