The men, one armed with a knife, stole a cash box from the vehicle on the Springfield Road around 12:50 pm today. No one was injured during the incident.
Police say the pair then escaped in a silver saloon car that was later found abandoned in Gortfin Street.
During follow up inquiries, detectives discovered that the two men made off with a sum of cash on foot in the direction of the Beechmount area.
Detectives have appealed for anyone with information to contact them on 101, the new non-emergency number, or anonymously through Crimestoppers on 0800 555 111.