The line has now been cleared but National Rail says trains between Rugeley Trent Valley and Walsall may still be cancelled, delayed or revised.
The disruption was expected to last until 4pm, however was cleared by 3.05pm.
It is currently unclear how many people were involved in the incident.
A spokesperson for National Rail said: "A trespass incident at Hednesford is resulting in all lines running through this station being blocked.
"Trains between Rugeley Trent Valley and Walsall may be cancelled or revised."