Network Rail called in firefighters to pre vent a "catastrophic" collapse that could have posed a risk to workers repairing the main Devon railway line.
A geologist is working with the fire crews and Network Rail's contractors.
Devon and Somerset Fire and Rescue (DSFRS) said crews were brought in after a large area - about 30m (100ft) - of soil and rock directly above the main line at Teignmouth Road appeared to have "slumped" over the past 48 hours.
"Network Rail are now unable to work beneath this area due to the potential for catastrophic collapse posing a risk to workers and causing further damage to the railway infrastructure," DSFRS said.