Timaru parents and caregivers have been warned by police to be on their guard after the suspected abduction of a nine-year-old boy.

The boy was found "in distress" and with facial injuries on Holme Station Bridge by a passer-by about 4pm, Thursday.  He was taken to Timaru Hospital, where he remains in stable condition.

The boy had left Oceanview Heights School in Selwyn St at 3pm and police are still trying to determine how he arrived at the bridge, 15 kilometres away.

Police believe the boy was abducted and Mid-South Canterbury area commander Inspector Dave Gaskin said investigators were hoping to speak to the child today.

"Taking advice from medical professionals, we have not engaged in an interview with the child before today," he said.

"We have to make sure that he’s well enough to speak with us."

Gaskin would not elaborate on the extent of the child’s injuries, and would not comment on whether there was any evidence of a sexual assault.  Police are also not saying whether they suspect the boy was abducted by a stranger.

The boy normally walked home after school, police have said. However, caregivers and schools would be wise to take extra safety precautions with children, Gaskin said today.

"If it was my child, I’d be a bit more vigilant right now."

Oceanview Heights School principal Jenny Langley said the school was advising parents to pick up their children or make sure they were not alone when they leave school.

There were extra teachers on gate duty "just to make sure we keep our parents informed", she said.

The boy was found wearing his school uniform - a dark blue polar fleece, dark blue shorts and a teal green polo shirt. His backpack was found near Holme Station Bridge on Friday.

Gaskin said police were working with Oceanview Heights School in the investigation.

A specialist team from Christchurch also completed a search of the site at the weekend.

Police will likely return to the area later today to stop vehicles passing through in hopes of turning up more leads, Gaskin said.

The boy is described as being of dark complexion, slim build, about 30kg, with dark hair. He is considered small for his age and police describe his height as more like that of a 6 or 7-year-old.

Langley said the school was supporting the family as best it could.

"This sort of event ... hits the community very hard. Because we are a small school everybody knows each other."

An assembly was held this morning reiterating the Keeping Ourselves Safe programme that is run each year in conjunction with the police.

The children were "fine", and staff were answering their questions as "truthfully as we can", Langley said.

"We have very few details at our disposal at this time."

Langley was confident the procedures at the school to protect children were as "tight" as they could be.

"Once children have left the school grounds we have no control over what happens after that. At that point you rely on the community at large to behave appropriately."

Anyone who might have seen the boy or suspicious activity near Oceanview Heights School or Holme Station Bridge should contact Timaru police on (03) 687 9808.

- © Fairfax NZ News