A joint police and fire investigation has been launched into the cause of a fire, which damaged the disused St Clement’s Hall in Lerwick.
Police are guarding the St Olaf Street building until officers from the mainland arrive in the isles to start their inquiries.
The owner of the building said he suspected vandalism was behind the outbreak.
A fire service spokesman said the fire caused serious damage to the extension of the former church on Monday night.
Crews from Lerwick and Scalloway had to use breathing apparatus to gain access to the building.
The fire was located on the ground floor of the property and firefighters had to contend with severe smoke logging, the spokesman said.
The 20 residents of King Eric House next door were able to remain in the care centre although evacuation had been considered.
A spokesman for Shetland Islands Council said: “No residents left the building. A senior member of staff received regular updates from police and fire service and at the end it was decided not to evacuate.”
St Clement’s was recently acquired by local businessman Malcolm Younger, who has plans to convert the church building into office space.
A retained fire fighter himself, Mr Younger said he first heard of the fire when his bleeper went off on Monday evening.
Yesterday he said the building was uninsured, adding he was convinced that vandalism was to blame.
He said: “I am shocked by this mindless vandalism. Although the damage is relatively minor it could have been so much worse.
“This has been a very selfish act considering there is a care home next door, which could have been affected had the fire spread.
“Whoever is responsible for this should be ashamed of themselves.”
The distinctive building was opened in 1911 and was used as the parish hall for Lerwick Parish Church for many years.
It was sold to Lerwick Town Council for recreational use in 1966. In the late 1990s it was regularly in use as accommodation for bazaar type stalls, most notably by budget retailer Chris Hodge.