Two US Army Black Hawk helicopters they collided during a training mission over Kentucky on Wednesday night, according to a US military statement.

The condition of the crew members was not immediately known, military spokeswoman Nodish Thurman said in a statement to Reuters early Thursday morning, without specifying the exact number of people on board.

However, Kentucky Gov. Andy Beshear said in a tweet that there were estimated to be casualties and that Kentucky State Police and the state’s division of emergency management were responding to the crash.

The crew members were aboard two Black Hawk helicopters that crashed at approximately 10:00 p.m. Greek time (0200 GMT Thursday) in Trigg County, Kentucky, Thurman said. The causes of the collision are being investigated.

“The administration is currently focused on taking care of service members and their families,” he said.