"They are joking about it a bit.
"The man shot a couple of bullets. One left a hole in the ceiling above the counter."
Detective Senior Sergeant Warwick McKee said a man entered the superette and threatened the woman with a handgun.
"The offender pointed a firearm at a female shop employee and demanded money from her, and fired a shot towards the ceiling," he said.
As he was running off with the cash, the woman hit the offender over the head with a broom handle.
"The offender may have an injury to his head or require medical attention," McKee said.
The offender was last seen running across Kilbirnie Park, between the Kilbirnie Aquatic Centre and the Poneke Rugby Clubrooms, about 1.25pm.
"Police would like to hear from any person who may have witnessed this incident or knows the identity of the offender."
Police are providing support and welfare to the woman.
"The unlawful use of firearms, particularly of a threatening nature, is of serious concern to police," McKee said.
"It is important that anyone with any information on the identity of this offender speaks to police."
The offender is described as a Caucasian man in his mid-20s, about 1.7m tall and of slender build. He was wearing black trousers and a long-sleeved black sweatshirt under a sleeveless orange high-vis vest.
Any witnesses or people with information should contact Wellington police on 04 381 2000 or Crimestoppers, anonymously, on 0800 555 111.