The Bomb Response Unit is investigating after a suspicious item was found in Roxburgh Park.
Police confirmed they were called to grassland near Lakeside Drive in Roxburgh Park about 12.40pm to conduct a safety check.
The Bomb Response Unit is currently on scene and nearby roads have been cordoned off until the area is deemed safe.
Metro and V/Line train services have been halted due to the police operation.
On the metro line, buses are replacing trains between Broadmeadows and Craigieburn.
Trains are being replaced by buses on the Seymour line between South Cross and Seymour and Shepparton.
On its website, V/Line said it anticipated coaches would be in operation until 5pm, with extended journey times of up to 60 minutes.