Police say public help will be crucial in helping them solve Geelong's latest armed robbery.

A man armed with a knife threatened the attendant at the North Geelong Apco on Saturday night, making off with an unspecified amount of cash.

He was wearing a hoody and cap and had a scarf over his mouth, and is described as being around 170 cm tall, Caucasian and of medium build.

Meantime the spate of armed robberies in Geelong has prompted calls for changes to the way service stations operate at night.

Locals people have contacted our newsroom with suggestions ranging from the hiring of security guards and extra staff, to fluorescent dies built into service station counters and an end to walk-in service after 11pm.