The cause of the semi-truck fire last Friday is still unknown but it is believed to be a mechanical issue.

An 18-wheeler caught fire Friday while headed east on U.S. Highway 10 near the Sauk Rapids water tower.

Sauk Rapids Fire Chief Tony Hommerding said the truck was being taken for a test drive when the driver noticed a smell and pulled off on the shoulder.

Flames engulfed the truck and the driver exited the vehicle and called 911. The driver was not injured and is believed to be the only occupant of the semi, Hommerding said.

Firefighters had the truck blaze under control within 10 to 15 minutes. The only vehicle involved was the 18-wheeler.

Because of the hot and dry conditions, the flames from the truck spread into the ditch and reached the fence near the orange, red and brown Sauk Rapids water tower.

Sartell Fire Department was called in to assist with the grass fire, Hommerding said.

Traffic was halted on the eastbound lanes but returned to normal within a short time. Westbound traffic was restricted to one lane while firefighters got the blaze under control.