SPOKANE VALLEY, Wash. -

The Spokane Valley Fire Department says a greenhouse fire that broke out early Wednesday morning was likely started by transients.

The fire started just after 4 a.m. at 6th and Chronicle in Spokane Valley.

A Spokane County sheriff's deputy was driving by and noticed smoke coming from the abandoned greenhouse. He called in the Spokane Valley Fire Department.

Firefighters quickly knocked down the flames. 

The fire department says there was minimal damage to the building. 

They say there appeared to be transient activity at the scene and that was likely the cause of the fire. 

An investigation is underway.