Firefighters took more than 12 hours to bring a blaze at a disused hospital in Inverness under control.
The fire broke out in the early hours (picture by HCVF television)
About 40 firefighters and six pumps attended the fire at the former Craig Dunain building in the Leachkin area of the city.
The building, which has lain empty for some time, was being refurbished.
A spokesman for Highland Fire and Rescue said the blaze, which began at about 0340 BST, was brought fully under control at 1545 BST.
Police have put a cordon around the building while structural engineers carry out an assessment.
A Northern Constabulary spokesman said the cause of the fire was still being investigated, however inquiries were at an early stage and proving difficult due to the dangerous state of the building.
About 40 firefighters tackled the blaze. Pic by Jimmy Addison
He added that it could be some days before investigators can gain access.
Insp Mike Coats said: "The alarm was raised in the early hours of the morning and police and fire service units attended the scene."
He said the fire had taken hold of a significant part of the building.
"The property is vacant and currently under renovation, and at this stage it is too early to say what has caused the fire," he said.
Police have appealed to anyone who saw anything of relevance, such as people or vehicles in the area, to contact them on 01463 715 555 or Crimestoppers on 0800 555111.