The forecourt attendant was shaken but not injured as a result of the robbery, the second of which he has experienced in recent months, police said.
The offender has not been identified and police would like to hear from any residents in the area around the service station who may have seen something, Detective Senior Sergeant Greg Standen said.
"The offender was observed loitering in the area prior to the robbery, so we are asking any people in the area around the time of the robbery, who may have seen something, to get in touch."
Anyone with information was asked to contact Whakatane police on (07) 308 5255.
Information can also be provided anonymously via Crimestoppers on 0800 555 111.