A Kiowa OH-58 D helicopter of the Croatian Air Forces crashed in the sea between the island of Zlarin and the coastal town of Zablace near the Adriatic city of Sibenik on Monday morning, the defence ministry reported on Monday morning.
A search operation for survivors is currently under way, and the ministry will issue new information later in the day.
The helicopter crashed during a training flight.
It is still unknown how many people were in the helicopter, the Sibenik city police said.
This story is breaking and will be updated.