A baby was found locked in a car with a note from its mother saying she had gone shopping and to call her if it needed anything.

Despite public outage after the photo of the baby was uploaded online, New Zealand police said they were not investigating the incident as there had been no formal complaint.

The baby was spotted alone in the vehicle in a car park in Porirua Pak'nSave in Wellington. An eyewitness told the New Zealand Herald: "It was written from the baby's perspective, and it said, 'My mum's in doing the shopping, call her if I need anything', and it had the cellphone number.

"We waited there for a little bit, wondering if the mum was just going to be two seconds and come back. And my wife said, 'I'm not going in without someone being here with the baby'."

The paper added two passersby waited by the vehicle after one of them called the mother to ask her to come back to her child.

Police spokeswoman Annie Coughlan said: "We don't know who the people are, we don't know the phone number, we don't know where to start.

"We would launch an investigation if we could but at this stage no one's come forward."

Sgt Justin Rakena of Porirua Police said "[Incidents like this] need to be taken on their merits and often it's a mum that's run into a shop, for example, and is only away for five minutes.

"Absolutely [it should be reported to police], but it doesn't mean to say we'd prosecute. I would suggest that the majority of people in that situation aren't prosecuted."

It is illegal in New Zealand to leave a child under 14 years old alone for a long period of time or in unreasonable conditions. Doing so could result in a fine of up to NZ $2,000 (£1,000).