Nine people have been killed in a crash involving two US Army helicopters in Kentucky, a military spokesperson said.

Nondice Thurman, a spokesperson for Fort Campbell, said the deaths happened the previous night in south-western Kentucky during a routine training mission.

A statement from Fort Campbell said the two HH-60 Black Hawk helicopters, part of the 101st Airborne Division, crashed at around 10pm on Wednesday in Trigg County, Kentucky.

The 101st Airborne confirmed the crash about 30 miles north west of Fort Campbell.

The crash is under investigation.

“Right now our focus is on the soldiers and their families who were involved,” the statement added.

Kentucky governor Andy Beshear had said earlier that fatalities were expected, adding that police and emergency officials were responding.

“The crash occurred in a field, some wooded area,” Kentucky State Police Trooper Sarah Burgess said at a news briefing. “At this time, there are no reports of residence damage.”

Fort Campbell is near the Tennessee border, about 60 miles north west of Nashville, and the crash occurred in the community of Cadiz.

Nick Tomaszewski, who lives about a mile from where the crash occurred, said he saw two helicopters flying over his house moments before the crash.

“For whatever reason last night my wife and I were sitting there looking out on the back deck and I said, ‘Wow, those two helicopters look low and they look kind of close to one another tonight’,” he said.

The helicopters flew over and looped back around and moments later “we saw what looked like a firework went off in the sky”.

“All of the lights in their helicopter went out. It was like they just poofed… and then we saw a huge glow like a fireball,” he said.

Flyovers for training exercises happen almost daily and the helicopters typically fly low but not so close together, he said.

“There were two back to back. We typically see one and then see another one a few minutes later, and we just saw two of them flying together last night,” he said.

Members of the Kentucky Senate stood for a moment of silence on Thursday morning in honour of the crash victims.

“We do not know the extent of what has gone on, but I understand it is bad and there has been a substantial loss of life of our military,” Senate president Robert Stivers told the chamber.

Last month, two Tennessee National Guard pilots were killed when their Black Hawk helicopter crashed along an Alabama highway during a training exercise.