"I don't know exactly what happened but apparently a mother accidentally left her baby in the car," the attendant said.
The attendant was unsure how long the baby had been left in the car, but said she hadn't heard any sounds of distress.
"I walked past just before and everything seemed to be okay."
A Northern police spokesman said they weren't aware of the incident and so couldn't comment on it.
Titirangi Fire Brigade officer Brett Goodhue said the baby girl was trapped inside the car for about five to 10 minutes.
"The woman's immobiliser battery in her car key had gone flat so she wasn't able to unlock her car," he said.
"We managed to jiggle the car key around and open it and get the baby out.
"It was quite hot in the car so if it had been left much longer we would have smashed a window to get the baby out."
The baby girl, who appeared to be less than 12 months old, was awake and looking around but didn't seem to be distressed, he said.
"It wasn't life or death. The baby was still quite cheerful when we got it out."
Avondale Fire Service was also on its way to assist but wasn't required, he said.
The woman went up the road to get new batteries for her car key and was then able to get away, he said.
It was 24C, fine and sunny in Titirangi when the baby became trapped.
A member of the public alerted the fire service to the situation, Mr Goodhew said.
"We're only about 50m down the road from the library so they just walked down and told us about it. I'm not sure whether they were a friend of the woman, or had just seen her worried about not being able to get her baby out of the car."
