The 12-year-old girl was walking alone on Bourke Street, near Mount Austin High School, about 8.15am on Tuesday when a man in his 30s ran up to her and grabbed her from behind.

Another man came to the girl's aid, shouting at her assailant from some distance and scaring him off.

Wagga police crime manager Detective Inspector Darren Cloake said any instance of a child being approached in the city was a concern.

“We reinforce with children walking alone and their parents to be vigilant,” he said. “We’re not immune to this.”

The girl ran to Mount Austin High School, where she is a student, and reported the incident to staff there, who contacted police.

Police are now investigating the matter and have launched an appeal to find the assailant, described as a man in his 30s, who was wearing a black hooded jumper and light coloured denim jeans at the time of the attack.

Inspector Cloake said people needed to be aware of their surroundings at all times when walking the city’s streets.

“If there are any concerns, they need to raise it with local police or school principals and we will act accordingly,” he said.

“If they are walking to school, they should do so in pairs or with an adult supervisor. It’s not just stranger danger, there’s road safety concerns relating to that.”

A spokesman for the Department of Education said the school had provided support to both the girl involved in the incident and the wider student body.

“The school commends the actions of the householder who intervened,” the spokesman said.

“Students were told of the incident and given advice on an assembly.”

In March, two girls, aged seven and 11, were approached in the space of a week coming home from school in Kooringal.