A Strathclyde Fire and Rescue spokesman said: "Five fire appliances, two major incident units with heavy rescue equipment and a technical support unit to deal with any potential hazardous materials and to minimise any environmental impact were mobilised as a result.
"Strathclyde Fire and Rescue personnel are working alongside personnel from the RAF, the police and ambulance services to deal with this incident."
Morag Campbell, from Arrochar, was with her partner when two jets passed over the village just before lunchtime.
"They were very, very low just above the tree line," she said.
"There was a terrible noise after they flew up the Rest and be Thankful and we both said at the time that it sounded like one of them had crashed.
"We couldn't believe it when we suddenly saw all the emergency services speeding through our village.
"I must say though that it was the lowest that I had seen jets travel through this area."
Sue Oliver, who works at Forest Holidays Campsite at Ardgarten, just past Arrochar, told the BBC the crash happened just before midday.
The Tornado F3 was based at RAF Leuchars in Fife
She heard two planes flying overhead between 1130 and 1200 BST.
Ms Oliver said a short time later someone came in to the site and told her there had been a crash.
Frances Bremner from Cairndow, a village to the west of Arrochar, described how she heard jets overhead.
"From about 11am this morning we at Loch Fyne Oysters have listened to these jets flying over and over again," she said.
"My daughter at home saw two jets go over the back of our hill at Cairndow. One was very high but the second very low and she said she hoped it would make it over the hill as it was so low.
"This area is known to have these jets fly over and they do seem to fly very low but you assume they know what they are doing and how risky it is. I hope the crew had time to get out."
The weather in the area at the time of the crash was said to be overcast with thick clouds.
Andy Graham, 60, a retired rigger who moved to Arrochar three years ago, said he saw two Tornados flying low in the area around lunchtime.
He said: "We get jets flying over here on training exercises quite regularly. It's not unusual to see them and you definitely hear them.
"But today they seemed to be flying much lower than normal. We watched them fly along the loch, up through the glen and towards the Rest And Be Thankful."
The Rest and Be Thankful is a tourist spot on the A83 Arrochar to Inveraray Road, north west of Loch Lomond.
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