A fire that destroyed 18 to 20 tons of hay on a parked semitrailer Friday night on Midland's Main Street is under investigation by the state fire marshal and Haakon County sheriff, according to Midland Fire Chief Rueben Vollmer.

The fire is being investigated as a suspicious fire, and arson has not been ruled out, Vollmer said Monday.

Flames were leaping 30 feet in the air by the time firefighters arrived, Vollmer said.

The tractor and trailer were located about 40 feet from a home and another structure.

The fire spread quickly through the bales, but firefighters managed to hold the fire down while the semitractor and trailer were detached, Vollmer said.

Tractors were used to push the smoldering bales off the trailer and down the street to a vacant lot.

The hay was still smoking on Monday, Vollmer said.

The fire caused about $3,000 to $4,000 in damage including the loss of the hay and damage to the trailer, Vollmer said.

Mechanical failure or an electrical failure on the trailer have been ruled out as the cause of the fire, he said.

"A suspicious vehicle was seen in the area prior to the fire," Vollmer said.

About 20 members of the Midland Volunteer Fire Department responded to the fire. Many remained on the scene throughout the night to monitor the smoldering hay.

Anyone who may have seen anyone around the parked truck and trailer Friday evening is asked to contact the Haakon County Sheriff's office, Vollmer said.