A fire broke out in a disused building in Springfield Hospital, Tooting, this morning.
A Wimbledon firefighter said the crew was called out to the hospital at 5am on Wednesday morning, and four engines attended the scene.
A spokesman for the station said: "The fire probably wasn't an accident."
One room was completely gutted in the fire, which spread quickly and caused smoke damage.
Metropolitan Police said enquiries were ongoing.
A spokesman from the hospital said: "A fire broke out at a small empty disused building in the early hours of this morning.
"Our staff acted fast calling the fire services who responded quickly.
"No one was hurt in the incident and an investigation is currently underway to identify the cause of the fire."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article