Australia's rail safety watchdog is looking into allegations raised in parliament by a federal MP that Metro's track maintenance standards are so shoddy it is putting public safety at risk.

Western Australian Labor MP Alannah MacTiernan alleged on Monday night that Melbourne's rail operator had let the city's railway tracks fall into such a dangerous state of disrepair a train could run off the rails.

Insiders say safety standards have deteriorated under Metro, with emergency 'fishplates', seen here at Alphington, used instead of new tracks.

She told parliament she had called on the Office of the National Rail Safety Regulator to investigate, and had supplied the watchdog with images of degraded rails around the Melbourne network.

A spokeswoman for the regulator confirmed late on Monday it was investigating claims put to it by Ms MacTiernan, who was WA Transport Minister for eight years before being elected federal member for Perth last year.