A New Jersey mother is in police custody after reportedly setting her baby on fire on Friday. 

Hyphernkemberly Dorvilier was arrested in Pemberton Township, about 30 miles from Philadelphia, after allegedly dousing her infant daughter with an accelerant and lighting her. The baby's age has not been disclosed. 

Witness Davis Joseph said that he saw a female take an item out of her car and burn it in the middle of Simontown Road. The woman allegedly told Joseph that she was burning dog feces. 

"She said it was poop," Joseph told NBC10. "She said her dog pooped in her car and she was burning the poop on the side of the road."

Joseph's wife heard the baby scream, and he saw an umbilical cord still attached to the infant. 

"It was just mind-boggling," he said . "It was a nightmare even if you have a strong heart."

Although initially calm according to reports, the woman soon tried to flee the scene. Joseph held her down, however, and police were called. The baby was still on fire when emergency officials arrived. 

Burlington County prosecutor spokesman Joel Bewley said the baby girl was still breathing when she was transported to a Philadelphia hospital. She died two hours later. An autopsy will be performed to determine the cause of death.

Mount Holly Fire Company Lieutenant Nick Allen said she wished the mother would have utilised the state's Safe Haven law. 

"I wish she would have taken better action on it, dropped her off at a hospital or fire company, called the state or police department to take care of the baby," he said. 

Prosecutor Robert Bernardi declined to say if Dorvilier had a criminal record, or if she had been investigated by child protective agencies. 

The 22-year-old was charged with murder on Saturday, and is being held on $500,000 bail. Police have yet to identify a motive.