A 20-tonne rock dangling above train lines in the Blue Mountains is causing significant delays for commuters as engineers work to remove the boulder.
The fallen rock appears to have detached from a large overhanging section approximately 20-25 metres above track level, Trains Info said via social media.
"A large rock identified today [Saturday] above the rail corridor at Glenbrook is being removed for the safety of customers and staff," the statement said.
At 7am on Monday, NSW TrainLink West said geotechnical engineers were on site working to secure and removed the 20 tonne rock.
"Until this is complete, we have plenty of buses replacing trains between Penrith and Springwood," the statement said.
"Real-time apps are up-to-date, please contact us for further assistance."
Transport NSW said buses were replacing trains between Penrith and Springwood due to emergency works at Glenbrook.
"Allow extra travel time, listen to announcements and check indicator boards or consider alternative travel arrangements," it said.