Four women were killed in a fire that ripped through the top floor of a Bronx apartment building Tuesday night, law-enforcement sources said.

The blaze erupted at about 7:20 p.m. in a sixth-floor unit of the building on Grand Concourse near East Mount Eden Avenue in the Claremont section, officials said.

After igniting in Apt. 603, the blaze quickly escalated to three alarms and ripped through the roof.

In all, 140 firefighters responded to the scene, the FDNY said.

“I was in the kitchen and the [fire alarm] was going off,” said resident Joy Murdoch, who lives in the apartment that caught fire with her 99-year-old mother, Victoria McDonald.

Murdoch was in the kitchen and her mother was in the living when she noticed the fire coming from her mom’s bedroom. She said the fire was likely caused by a space heater her mother had turned on earlier.

“I walked over and I see the flame was coming up,” Murdoch said. “The flame was red hot. The heat penetrated [everything].”

Murdoch said her mother “didn’t want to go! She didn’t take it seriously!”

The four critically burned victims were transported to the nearby Bronx Lebanon Hospital, where they were pronounced dead, a police spokesman said.

They were found inside neighboring six-floor apartments — two in each unit, according to the sources. Their identities were not immediately revealed.

A fifth person suffered minor injuries, an FDNY spokesman said.

Murdoch, was finally able to escort her mother out, then ran back upstairs to fetch their dog.

“I wasn’t afraid. I was just trying to get my mother out! She was stubborn and didn’t want to get out!” said Murdoch.

Her mother was taken to Bronx Lebanon Hospital, where she was in stable condition.

Video posted to social media showed flames raging through the windows of the corner apartment, with firefighters’ hook-and-ladder rigs out front.

The blaze was declared under control at around 9 p.m.

Bronx City Councilman Ritchie Torres offered his condolences to the victims and their families.

“Please keep their families in your prayers,” Torres tweeted He also thanked the firefighters “for their valiant acts of public service.”

The proximity of the fire to Bronx Lebanon Hospital had some fearing online that the blaze was there.

“Damn Lebanon hospital in the Bronx is on fire . . . prayers up,” one man wrote.

The fire is still under investigation, although sources confirmed to The Post that probers were eyeing the space heater as the cause.