All lines were blocked between Weymouth and Dorchester South due to a fault with a set of points.
Train services running to and from these stations may be delayed or revised.
Disruption is expected until approximately 1pm.
A spokesman for South West Trains said: "A fault with a set of points means that trains are currently unable to run between Dorchester South and Weymouth.
"This does not affect GWR services which run between Dorchester West and Weymouth, however please be advised that this is a limited service.
"Staff are on their way to examine and rectify the fault but in the meantime, trains will not be able to run beyond Dorchester South.
"If you are at Weymouth or Dorchester South, please approach a member of staff for assistance.
"If you are at Upwey, please press the blue information button on a Help Point, which can be found on each platform.
"We are sorry for the disruption to your journey today."