Fire investigators could take weeks to identify the cause of the blaze which badly damaged historic Alston Hall.
The roof was all but destroyed in the inferno, with towering chimney stacks and a gable end wall all suspected of being unstable.
A spokesman for Lancashire Fire and Rescue admitted: “Safety is our prime concern and until we can be sure lives will not be put at risk no-one can go in there.
“We won’t know how the fire started until investigators can access the building. That could be days, weeks or even months.”
The hall’s owners who are members of the Patel business family from Preston looked on anxiously as firefighters were damping down following the devastating blaze yesterday.
They declined to talk about the incident which badly damaged the roof and top floors of the Victorian mansion.
But, as he drove away, one man, thought to be a family member, declared to waiting reporters: “We’ll be back stronger than ever.”
The blaze broke out in the Grade II Listed building at around 10.30pm on Wednesday night.
The alarm was raised by two astronomers who were viewing the planet Jupiter from the UCLan observatory nearby.
Researcher Dan Holdsworth said they had become suspicious when smoke started wafting across their telescope.
When they spotted the fire they called 999.
Fire crews from across Lancashire raced to the country hall near Longridge and, at the height of the blaze, there were 10 appliances, plus two aerial ladder platforms and a mobile command centre at the scene.
The brigade also called in a specialist drone team to survey the damage from above.
Incident Commander Shaun Walton told the Post: “When our crews arrived there was a significant fire involving the roof space and the first floor of the building.
“With it being such a large building and with the extent of the fire we felt it more appropriate to deal with it overhead from two aerial ladder platforms to make it a safer working environment for our firefighters.
“Because it was well-established it wasn’t a case of firefighting, it was a case of containing it.
“Our crews did very well to prevent it spreading to the remainder of the building.
“The significant heat caused columns and beams to collapse and there was a lot of structural instability of chimneys and gable ends.
“We couldn’t commit our staff into the building or its immediate perimeter because there was concern the structure was unstable and could collapse.
“The cause is under investigation.”
Another brigade spokesman said: “We had around 75 firefighters at the scene at the height of the incident. Four fire engines remained there all yesterday and we will probably be returning today. We have still not entered the property.
“There are still bits of debris dropping and it is just too dangerous to send firefighters in there while there is a potential for debris to fall on them.
“The fire investigation will have to wait until it is safe enough to go in.
“We don’t know how long that is going to take, but it could be several weeks, even months. With the dangerous state of the building our main concern now is making sure everyone is safe.
“There is a structural engineer down there and he will decide whether it needs to be shored up before anyone can go inside.”