A police vehicle passes Trentham School, in Moonshine Rd, Upper Hutt, on Wednesday, after reports of an attempted abduction on Monday.

Schools in Upper Hutt are on full safety alert after another attempted abduction of a child.

A boy walking home from Trentham School on Monday was asked to get into a stranger's car, but ran away after the man failed to provide a password the family uses when sending people to pick up the boy.

The incident follows a similar one at Upper Hutt School on March 28, and is the fifth of its kind reported in the city in the past several weeks.

Trentham School principal Suzanne Su'a said the boy, an older pupil at the year 1-6 school, was approached by a man in a car who said: "I need to take you home."

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The boy asked the man for a safety password, which he answered incorrectly.

"The child ran off and didn't tell his mum, as he didn't want her to worry," Su'a said in information to parents on Tuesday.

"He has told us now, as he's afraid to walk home this afternoon."

She said the password strategy was based on Ministry of Education advice.

The man was in a black car in front of the Upper Hutt College netball courts in Moonshine Rd, several hundred metres from Trentham School.

"We will have more staff out in the playground and on Moonshine Rd after school for the rest of this week," Su'a said.

"We don't want to alarm students so they are frightened to go home, but we will remind them about what they need to do to keep safe."

Hutt Valley police confirmed three recent incidents.

In the first, on March 13, the person involved had been identified and no criminal element was involved, Detective Senior Sergeant Mike Sears said.

An investigation of the Trentham incident was under way.

"Police are reviewing evidence and at this stage cannot confirm if there is a link between any of the incidents," Sears said.

"Patrols have been increased in the area and the schools and families involved are being spoken to, and we are working closely to support them.

"Following an incident outside Upper Hutt Primary School on March 28, specialist interviews have been conducted with the young person involved and police are currently reviewing the information that has resulted from that."

Upper Hutt schools had been reinforcing safety measures with students and communicating concerns to parents and caregivers.

"We are alarmed by the frequency of these incidents and feel it is necessary to inform our community," Maidstone Intermediate principal Mary O'Regan said in information to parents.

"Since the beginning of March, in the Upper Hutt area, there have been five incidents of students being approached by someone attempting to pick them up in a vehicle.

"The police tell us that one has been found to be quite innocent, but the others are unresolved.

"Teachers have discussed with their students how to keep safe from these predatory offenders. I recommend you reinforce this at home and have a conversation about strategies to use if they are approached.

"While we do not adhere to the notion of 'wrapping children in cotton wool', this is a timely reminder of the importance of giving children strategies to use should they ever need them."