DOVER — A Thursday morning house trailer fire was being investigated as an arson, the Delaware Office of the State Fire Marshal said later in the day.

The blaze, reported shortly after 11 a.m., occurred in the unit block of East Pinewood Drive near South State Street, spokesman Assistant State Fire Marshal Michael G. Chionchio said. The Dover Fire Department responded to the call and arrived on the scene with an active fire.

State fire investigators were called to the scene to conduct the investigation. The fire was deliberately started inside the house trailer, authorities said. Deputy fire marshals developed significant leads, Mr. Chionchio said, and were pursuing those leads in an effort to make an apprehension.

Heavy fire damage was estimated at $30,000. One person was transported to the Kent General Hospital in stable condition for lacerations.