Clean up efforts continue after a train derailment in Saint John early Tuesday morning.

Four cars that were carrying potash went off the tracks that run parallel to Crown Street about 12:30 a.m and flipped onto their sides, spilling some potash on the ground, New Brunswick Southern Railway spokeswoman Mary Keith said in an emailed statement.

An additional eight cars went off the tracks, but remained upright.

"There were no injuries and the train was not carrying any dangerous goods," said Keith.

"There are no environmental issues and no roadway is obstructed."

Investigators are trying to determine the cause, said Keith.

As of 4 p.m., the four flipped cars remained on their side, but six of the eight derailed cars were back on the rails and moving. The other two were expected to be back on track by 8:30 p.m.

Removal of the spilled potash and delivery to the potash terminal was ongoing as of 7 p.m., said Keith.

The track is expected to be operational by mid-afternoon Wednesday, she said.

CN was moving 37 rail cars with three locomotive engines to the potash terminal on the east side of Saint John via a side rail spur that is maintained by the New Brunswick Southern Railway when the derailment occurred, said Keith.

The rail spur in question is dedicated exclusively to the movement of potash, she said. The impacted rail cars were at the tail end of the CN train.

Officials with Transport Canada's regional office in Moncton, the Transportation Safety Board and the provincial Department of Transportation have been notified.