Some 58 firefighters have been called to a blaze at Chase Farm hospital in north London.
London Fire Brigade said eight fire engines were sent to the scene on The Ridgeway in Enfield at just after 10.10pm on Sunday.
They discovered a small part of the ground floor of a two-storey building alight.
Crews from Enfield, Southgate, Edmonton, Chingford and Barnet fire stations are at the scene. The cause of the fire is not yet known.