Crews from stations in Gosport, Fareham. Portchester, and Southampton, as well as an aerial platform from Southsea Fire Station, were called to Anglesey Lodge in Anglesey Road, Gosport, at 7.30pm last night.
More than 20 firefighters were there for two hours tackling the blaze, which damaged an exterior wall of the early 19th century building.
It is the latest in a series of fires that firefighters believe have been deliberately started by trespassers.
A firefighter from Gosport Fire Station said: ‘I think we have been called out there four times in the last month.
‘The owner has put up fencing and razor wire, but kids find a way to break in.
‘It’s an ongoing eyesore.
‘There is a basement in the building and our worry is that some kids will get trapped in there and be seriously injured or die.’
No one was injured in the latest fire, with a large number of firefighters in attendance due to the complex layout of the building, according to the attending firefighter.
Photographer Dan Harbut, from Lee-on-the-Solent, who was passing the building when he saw it alight, said: ‘I was told by the fire brigade that it’s a listed building which is why so many different crews were sent, the site is regularly being broken into by people to explore the abandoned buildings and they have really increased the security at the site lately but is still accessible in areas.’