An investigation has been launched after a former chemical works was severely damaged in a fire.
The disused two storey building on Nook Lane was well alight when fire crews arrived on the scene at 12.45pm on Friday.
Two hours were spent tackling the blaze in Oswaldtwistle.
A spokesman for Lancashire Fire and Rescue Service said: "We required breathing apparatus and an aerial ladder platform and breaking in tools. The roof was destroyed and contents severely damaged on the ground and first floor.
"We are going to be monitoring the situation and are treating it as suspicious."
The fire broke out on Friday, December 16.
Police have been made aware of the matter.