Since I cannot turn off the source VM because it is currently in use in a production environment, I have to use the following steps to create a mirror VM in another project:
1) Create a snapshot of the boot disk of the source VM
2) Create a disk based on this snapshot in the target project
gcloud compute disks create vm-prod-disk --source-snapshot \
https://www.googleapis.com/compute/v1/projects/<source-\
project>/global/snapshots/<source-vm-snapshot> --project target-project
3) Create a VM based on the new disk from step 2
gcloud compute instances create vm-prod-duplicate \
--project target-project --disk name=vm-prod-disk,boot=yes