The Public Transport Authority is investigating whether millipedes are to blame for an incident on the Joondalup train line which left several passengers with minor injuries.

A slow moving train bumped into the back of a stationary one at Clarkson station about 6:30 am.

Several passengers have reported sore necks following the incident.

The PTA's David Hynes says large numbers of millipedes could be one of the factors behind the incident.

"It's happened to us a couple of times where there's been an infestation of millipedes where they've crossed over a track early in the morning after there's been heavy dew," he said.

"The first train or trains that come through crush the millipedes that are on the track, which makes the track slimy and therefore the trains can lose a bit of traction.

"It's a very serious issue for us, fortunately it was not a serious impact.

"Having said that, there were a number of people, I'm not sure whether they were knocked over, but a number of people have reported to us that they've got stiff necks rather than any bruises and certainly no breakages."