Crew members were flying two HH-60 Black Hawk helicopters, operated by the 101st Airborne Division, when the aircraft crashed late on Wednesday over Kentucky's Trigg County, Fort Campbell's public affairs office said.
A Fort Campbell spokesperson said nine soldiers were killed but provided no further information.
A news briefing was planned at the base for later in the day.
The HH-60 is a variant of the Black Hawk helicopter designed to provide support for various military operations, including air assaults and medical evacuations, according to the army.
During a congressional hearing in Washington DC, Army Secretary Christine Wormuth spoke about the crash.
"Thank you for your comments and thoughts and prayers for the families of our soldiers who were killed in the crash. Our hearts go out to them," Wormuth told the Senate Armed Services Committee.
"It's a heavy day for the army."
Kentucky Governor Andy Beshear travelled to Fort Campbell "to support our troops and their families after last night's tragic incident," he wrote on Twitter on Thursday.
The weather in Fort Campbell area, which straddles the border between Kentucky and Tennessee, featured clear skies and calm winds on Wednesday night, according to National Weather Service forecaster Marc Chenard.
23°C