Two people had to escape from their flat above an Indian restaurant after arsonists struck.
The pair were asleep when the fire started at 0430 BST at the entrance to the flats at the back of the Indis restaurant in Bournemouth.
Dorset Police have cordoned off an alley leading to the scene behind Seamoor Road in the Westbourne area.
The two residents were checked for injuries by paramedics, but are not thought to be hurt.
Police said the fire did not appear to be racially motivated.