An 83-year-old allegedly slashed two people with a machete — leaving a 5-inch gash in one man’s neck — during an argument at a raucous party in Williamsburg, cops said.

The elderly man was arguing with the woman, 28, and the younger man, 35, around 2 a.m. at 10 Scholes Street near Union Avenue in Brooklyn when he swung the long blade, slashing the woman in the forehead and the man in the neck, cops said. 

They victims were in stable condition but the man required about 30 stitches, police sources said.

The octogenarian was taken into custody at the scene, where the machete was recovered. His identification was pending charges, cops said.

The woman was taken to Woodhull Hospital and the man was taken to Elmhurst Hospital.

The attacker was brought to Kings County Hospital for a cut to his hand that may have been self-inflicted, cops said.

It wasn’t clear what the dispute was about, cops said.

The building where the knifing happened sits on a quiet street but it is known for raucous gambling parties, a neighbor said. 

The neighbor, who asked to remain anonymous out of fear of retribution, said the building has been a problem for years.

“This is not the first time,” they said. “Every time we call the police, the police is coming and nothing. Every time it’s fight, every time we got problems here.” 

The resident said there is constant noise from the basement parties. 

“They fight, they throw bottles, they talking and talking,” the neighbor said.  “It’s terrible. I don’t know exactly what’s happening down there. It’s illegal. It’s a big space, he got people playing cards there, other games.”

Police said the stabbing was the first time they went to the building in September, a spokesman said.