The damage caused by the B6344 landslip has extended to the adjacent Cragside estate with several unstable trees removed.
The Boxing Day landslide has closed the road between Rothbury and Weldon Bridge at Cragend, where it borders the southern edge of the Cragside estate.
The damage has progessively worsened in the past seven weeks and most of the roadway has now collapsed.
And a spokeswoman for the National Trust said that they have noticed movement on the estate since the initial slip in December.
A National Trust spokeswoman said: “The landslip on the B6344 was obviously an unwelcome development for the local area and the people who live and work here.
“A week or so after it happened, we started to notice movement on the Cragside estate, which we have been monitoring very closely.
“That movement has affected the stability of a few trees which have consequently had to be removed.
“We are assisting Northumberland County Council in any way we can as they investigate the precise nature of the slippage.
“It is fortunate that the B6341 offers ready access to Cragside and Rothbury so it’s business as usual for all of us.
“Indeed, the B6341 route offers the most stunning views of the surrounding landscape, which makes this part of Northumberland such a fantastic place to visit.
“It is, of course, vital that the B6344 is repaired as soon as is possible, although that willclearly take some time. Northumberland County Council has clearly made it one of their highest priorities for which they should be applauded.”
Estimates for the repairs suggest it could cost up to £3million and the county council has submitted an application for pinch-point funding from the Government.
Two weeks ago, the council’s corporate director of local services Barry Rowland described the repairs as a priority for the council.
A diversion is in place via the B6341 and illuminated message signs on the A697 give advanced warning of the closure.