Police have started working with Child, Youth and Family to identify the mum who left her newborn in the car while she went grocery shopping.
A photo of the infant, which was wrapped in a blanket in a car seat with a note for passers-by to call if there were any issues, was taken outside a Porirua supermarket on Saturday morning.
The mother's cellphone number was left on the note.
Senior Sergeant Justin Rakena from Porirua police said yesterday he could do nothing about the incident until someone complained.
"We weren't called, and we've had no complaints," he said.
"If they do call us, we'll be acting on it.
"We were never called at the time, so we've got nothing to go on. We'd look at it like we look at anything."
But police spokesman Nick Bohm said they would start making other inquiries today.
"The comments made yesterday were referring to pressing charges," he said this morning.
"What we will be doing is working with Child Youth and Family so we can identify the mum and get some social workers involved with her so she gets the support she needs.
"If the same situation started happening again and again, we would have to re-look at that."
He said police could make inquiries from Facebook posts and photos, but could not launch a criminal investigation.
Rakena said children being left alone in a car happened frequently in the area.
"I don't know what the stats are, but anecdotally you might have a kid left in a car once a fortnight, something like that," he said.
"This is quite common, and quite often there's an innocent explanation. At a guess I'd say 95 per cent of these things can be explained away."
He said it was not acceptable to leave a person under 14 unaccompanied, but more often than not it just warranted a warning.
It is illegal for a parent or guardian to leave a child under the age of 14 alone for an unreasonable time or in unreasonable conditions. Doing so could result in a fine of up to $2000.