Security sources say there is a "strong likelihood" that the explosion near Loch Lomond is linked to terrorism.
As revealed exclusively by STV News online, a member of the public reported hearing the blast in the Garadhban Forest area of Gartocharn, to the south east of the loch, at around 12 noon on Wednesday.
Specialist officers from Strathclyde Police are now carrying out a fingertip search at the site of the explosion in the woodland area about 300 to 400 yards from Ross Priory, a landmark 19th century building used for weddings.
The first aerial shots of the scene, obtained by an STV News helicopter camera, reveal police are examining a wide area of woodland with forensic work being carried out on woodland and undergrowth.
Now sources have told ITV News that there is a "strong likelihood" of a terrorist link.
They say from the amount of damage it is clear that someone with the ability to build and initiate a powerful bomb is responsible.
Strathclyde Police are being assisted by a team of counter-terrorism officers to establish the full circumstances surrounding the incident. The Northern Diving Group - the Royal Navy's equivalent of the bomb disposal squad - were called in.
Speaking on Friday afternoon, Chief Superintendent Calum Murray, Strathclyde Police's divisional commander, Argyll, Bute and West Dunbartonshire said: "The priority yesterday was to make sure that there was no risk to the public or officers in order that initial investigations could take place.
"We can assure everyone that this area is secure and there is no risk to anyone living, working in or visiting the area."
He added: "Today we are in the course of beginning a painstaking fingertip search. That is a significant undertaking. That will take a while."
He said: "Broadly you are dealing with an area of woodland in which felling has been taking place and there's wooding operations.
"Clearly we've got a centre of operations that we are focusing on and what we need now, having identified the area we are interested in, is to make sure the entire area is safe.
Mr Murray said officers from the Metropolitan Police were helping the investigation. He said: "In terms of other agencies, as you would expect we've got people with experience with explosives."
LOCH LOMOND EXPLOSION