A semi-truck driver carrying a load of hay bales ran into some trouble Sunday afternoon after the hay bales caught on fire.  

The driver was heading west on Highway 200 Sunday afternoon when troopers tell us the hay bales caught on fire.

Montana Highway Patrol Trooper Luke Burson says they believe the fire started due to heat coming off of the exhaust.

We’re told the driver of the semi-truck was not injured but the incident held up drivers for nearly three hours because both lanes of the highway had to be closed so fire fighters could put the hay bales out.

Missoula resident Michelle Gustafson says she was on her way to Seeley Lake with her parents when the trio saw smoke coming up on the highway ahead.

Gustafson tells NBC Montana when they got near the wreck she saw folks on the highway run to a nearby house, grab a garden hose and assist the semi-truck driver who was attempting to put the hay bales out.  

“It was really scary because we didn't know what he (semi-truck driver) was doing,” she says.  “He was in the semi, than he got out of it and tried to pull stuff away from the part that was attached with the hay bales.”

Gustafson says she’s seen her fair share of highway accidents, but nothing like this.  She tells us she’s just glad that the driver of the semi-truck is okay.  

“I'm just really glad that it didn't explode and that everyone's okay,” she tells us.  “It was just really scary how close people were to the flat-bed the entire time but I’m just glad that nothing bad happened.”

Troopers tell us Motor Carrier Services is doing a full investigation into the incident.