The landslide opened up between Brithdir and Tirphil in the Rhymney valley A landslide has brought trains to a halt between Bargoed and Rhymney in Caerphilly county.
Gwent Police received reports on Wednesday night that a large hole had opened up near the railway line and road between Brithdir and Tirphil.
The landslide was said to have brought down power cables and caused a hole in the banking.
A section of road is reported to have been washed away, exposing a gas mains supplying 15 properties.
Wales and West Utilities said the incident was caused by stormwater overwhelming a culvert.
However, the gas main was not damaged and supplies to customers are not affected.
The utilities engineer who went to the scene reported that the damage to the road has also exposed an old mine shaft.
Excavations were made further along the road so the gas main can be cut off at short notice if necessary.
Further investigations with other agencies will be made this morning, Wales and West Utilities said.
Train services have been stopped but there is a replacement bus service operating between Bargoed and Rhymney.
It is not known yet when a normal service will resume.
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