A man in his 30s was slashed multiple times while drinking with a group of pals inside a Brooklyn apartment early Friday, police said.

The victim was inside the building on Kings Highway near East Third Street in Sheepshead Bay when one of the four men he was with, who is also in his 30s, suddenly slashed him in the neck, arm and torso at around 4:40 a.m., cops said.

The man was rushed to Lutheran Medical Center, where he was listed in serious condition.

It was not immediately known what provoked the attacker, who is still at large, to slash the man.