A pair of longtime Brooklyn residents were killed Saturday when fire tore through their Flatbush apartment, police and neighbors said.

The victims, an 86-year-old woman and a 65-year-old man, lived on the second floor of the Nostrand Avenue building near Cortelyou Road where the fire began in the early morning, officials said.

Two women, an 82-year-old and a 40-year-old, suffered serious injuries and were taken to University Hospital at Downstate, police said. They were expected to survive, officials said.

A man who lives in the building next door and shares a wall with the fire apartment told The Post he heard arguing before the blaze.

Edwin Savaille, an accountant, said the argument was around 5:45 a.m. and woke him up.

“It was in Spanish, so I couldn’t understand what they were saying,” Savaille, 48, said. “But you heard the loud voices for sure. So it was definitely an argument going on.”

He went back to bed, and 30 minutes later was startled out of bed by screaming, he said.

“I heard someone on the block screaming, ‘There’s  a fire out here,’” he said. 

“So I looked out my window to my left — big flames coming out. So I got my family out, pets, everyone out.”

He praised the FDNY.

“They saved two people … two people might have perished,” he said. “So it’s been a crazy Saturday morning.”

The fire, which was under control by 7:38 a.m., is under investigation, the FDNY said. 

The victims have not been publicly identified, pending family notification, the NYPD said.

But they were identified by neighbors as a mother-and-son who have lived in the neighborhood more than 40 years.

The mother, Maria, had been bedridden for nearly 20 years and her son Jose cared for her, locals said.

The victim used to work as a tailor and Jose coached for a little league baseball team called the Bonnies, neighbors said. 

Jonathan Ortiz, 47, works at the corner store and said Jose came in frequently to buy food for his mom.

“He would come in every day to buy lunch for him and his mother,” Ortiz said. “He’d buy soups and whatever she could eat. He took care of her.

“Everyone in the neighborhood loved them,” he said. “Everybody is devastated.  Everybody is sad. The whole neighborhood is down.”

The fatal fire came a day after at least one man was killed and two firefighters seriously hurt during an explosion at a dry dock on Staten Island that left about 30 others hurt.

The cause of the Staten Island explosion had yet to be determined Saturday.