Josip Brozicevic, the head of the national mountain rescue service, said first responders had located the crash site in the Cikola river canyon near the central Croatian town of Drnis.

"The bodies of two crew members were also found," Brozicevic told AFP.

"The search for the third crew member is ongoing," he added.

Hungary's military also confirmed the crash, saying two helicopters had been participating in a training mission when the incident occurred due to "unknown circumstances".

"The Hungarian Defence Ministry has immediately started notifying the families," the military said in a statement.

Croatia's armed forces said it had mobilised a plane and helicopter to help survey the area where the helicopter went down.

Croatia joined NATO in 2009 and frequently hosts military exercises with partner nations in the alliance.