The crash happened around 10:38 p.m. near mile marker 30.
Police say five of those killed were in a van.
The names and ages of those who died have not been released pending notification of family, according to the Bowling Green Daily News.
Two tractor-trailers were also involved.More news: 'Dizzy' Vettel stopped shield trial run early
Six people were killed in a chain-reaction crash involving four vehicles including two tractor-trailers on an interstate highway in Kentucky, police said Friday.
The tractor-trailer drivers were treated at the scene for injuries and released, Hodges said.
Master Trooper Jeremy Hodges, spokesman for the Kentucky State Police Bowling Green post, said a commercial vehicle and two passenger vehicles behind it were stopped in the right lane due to congestion.
"A preliminary investigation of the collision has revealed the accident which occurred at the 30 mile marker of Interstate 65, happened at a particular portion of Interstate 65 where road construction was being conducted, and the roadway merges from three lanes of travel into two lanes", according to the press release. He said authorities are working to notify the victims' family members and make positive identifications.
All lanes of northbound I-65 were closed for hours in the area of the crash before being reopened.