The helicopters, from the 101st Airborne Division (Air Assault), crashed at around 10 pm Wednesday in Kentucky's Trigg county, northwest of Fort Campbell, the army base said in a statement early Thursday.

"We can confirm two aircraft from the 101st were involved in an accident last night resulting in serval casualties," the 101st Airborne Division tweeted later.

"Right now our focus is on the soldiers and their families who were involved."

Kentucky Governor Andy Beshear had said earlier that fatalities were expected.

"We've got some tough news out of Fort Campbell, with early reports of a helicopter crash and fatalities are expected," he said on Twitter.

He said Kentucky police and emergency management were responding.

"Please pray for all those affected," Beshear tweeted.

Fort Campbell said the incident was under investigation.

"More information will be released as it becomes available," it said.

Fort Campbell is home to the 101st Airborne Division, the US Army's only air assault division.

Nicknamed the "Screaming Eagles," the division was activated in August 1942 and gained renown during World War II in the D-Day landings and the Battle of the Bulge.

More recently the division has seen action in Iraq and Afghanistan.