A “soulless” mother shockingly killed her 20-month-old son in the bathroom of a Midtown burger joint Monday — and prevented restaurant workers from rescuing the doomed boy, police and witnesses said.

Then she “blamed the devil,” a police source said.

The 35-year-old Lower East Side mom, identified as Latisha Fisher, took little Gavriel Ortiz-Fisher inside a rest room at 5 Boro Burger on Sixth Ave. at 36th St. around 2:25 p.m., cops said.

As the tragedy started to unfold, a woman walked into the bathroom and saw the mother holding her hand on the boy’s mouth, but Fisher told her: “I put my hand over his mouth to put him to sleep,” according to a police source.

At some point, the mother locked herself in the bathroom. Customers and employees eventually became worried when the line to the toilets grew long.

When workers forced their way inside, the child was unconscious and foaming at the mouth, according to the sources.

hey said Fisher tried to swat away attempts by the restaurant staff to perform CPR on the limp toddler.

“I would describe her as soulless,” a law enforcement official said when asked if the mom seemed distraught. “She put her hand over his mouth and smothered him.”

Another sickened police source said: “She is a lunatic. She is crazy.”

Gavriel was rushed to Bellevue Hospital, where he died, cops said. The mother was taken into custody at the scene. Charges against her were pending early Tuesday.

“It’s hard, it’s really unbelievable. I know my daughter loves her son,” said the boy’s maternal grandmother, Merial Fisher, 54, as the fought back tears. “I don’t know what happened. It’s just so sad.”

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