The plane, believed to be from RAF Leuchars, in Fife, hit a hillside in Argyll.
No civilians are understood to have been hurt.
It is not known whether the two people on board - a pilot and a navigator - were able to eject from the aircraft safely.
An ambulance spokeswoman said two crews are at the scene.
A specialist operations team is also on its way.
The Tornado F3 is thought to have come down near a tourist spot known as the Rest And Be Thankful on the A38 Arrochar to Inveraray Road, north west of Loch Lomond.
A Strathclyde police spokeswoman said: "We can confirm that police were called at 11.45am to a report of a plane crash near the Rest And Be Thankful, Arrochar.