Five fire crews were called out to deal with a fire on the top floor and roof of the St Edmund’s Hospital site in Northampton last night.
A 999 call was made to at 10pm after smoke began issuing from the roof of the building, which is in Wellingborough Road.
At first firefighters had trouble accessing the site because of the security fence.
Once on the scene, they told all nearby resident to keep their doors and windows shut.
Although access to the building was limited to the unstable structure, by 11.30pm fire crews started to report good progress with tackling the fire.
They eventually left the scene in the early hours of Monday morning and have since returned at 7am to assess the damage. They are due to come back again at about 11am.
A fire service spokeswoman said: “It is believed to be deliberate at this stage. There’s nothing to suggest any other reason.”
Last night’s fire follows a blaze on Saturday, April 2.
In June 2015, plans for a care village were approved, however document from the developer justifying plans to demolish the Grade II listed former school house and nurses’ home has not been forthcoming.