The train was stopped north of Rolleston where it was checked and the cause of the sparks identified.
Norris said the train has been cleared and has now continued on its way south.
He said the cause could've come from a range of issues, including wagon brakes jammed on or hot exhaust fumes.
KiwiRail South Island General Manager Operations Jeanine Benson said it involved a freight train that was stopped as soon as the fires were discovered. There were no injuries and no damage to the train.
"The fires have been extinguished, and we are investigating the cause," she said.
"The closure was a precaution and the line has now re-opened."
Main South Rd was closed for a short period but is now open to traffic in both directions, Christchurch Transport Operations Centre (CTOC) said.