One person died and four others were sickened by suspected carbon monoxide poisoning Saturday morning in Brooklyn, authorities said.

The five people were believed to have been squatting inside a building that is up for sale on Jackson Street near Woodpoint Road in Williamsburg around 6:10 a.m. when they were found, cops said.

Investigators were working to determine whether the noxious gas was caused by a generator found at the location, an FDNY spokesperson said.

One victim, a man in his 40s, was discovered on the second floor and was pronounced dead at the scene, police said.

The others — two men, ages 24 and 50, and two woman, ages 25 and 30 — were taken to NewYork-Presbyterian Brooklyn Methodist Hospital for evaluation.

Realtor Anthony Testaverde has been working to sell the property, which has been riddled with the unwelcome guests for more than a year.

When he last visited the home, about six months ago, he noticed an air condition, a television and a generator had been set up inside the house.

Testaverde said he previously “went through the legal channels” to stop squatters from staying there, but they’re “still waiting for that to happen.”

“It’s New York City. That’s your mayor,” Testaverde griped. “We tried to get them out. There’s no electricity. There’s no running water. So he let them live in these conditions. So, shame on him.”