Two people, one armed with a shotgun, arrived at the Mobil petrol station about 1.25am and demanded to be let inside.
The two people working at the petrol station retreated to a locked back office, police said.
The offenders got in after smashing a glass panel in a door then fired a shot in an attempt to get access to the counter area.
They took the till drawer and tobacco products, police said.
CCTV footage revealed the face of one of the offenders when his mask slipped below his nose.
They left in a white Nissan.
The first service station hit was on Good Friday in Apirana Ave in Glen Innes, about 4.9km from Wednesday's robbery.