A young child infected with Covid-19 on Auckland's North Shore was in class right up until the school was closed this week.

All the nearly 600 families and staff at Glamorgan School in Torbay have been ordered to stay in self-isolation - and vigilantly watch for signs of sickness.

Work is under way to identify close contacts of the pupil, including classmates and staff.

The school is now closed until Monday with Auckland Regional Public Health Service warning it might remain closed next week if other cases are confirmed there.

It is understood other children at the school were off sick in recent days, with their parents reporting they were suffering Covid-like symptoms.

Boy, 6, infected attends Southern Cross Campus

The Torbay primary is one of three additional schools that have cases confirmed across Auckland last night.

They include Southern Cross Campus and Taeaofou I Puaseisei Preschool in Mangere East.

At Southern Cross a boy, 6, is infected with Covid.

The school's board was informed late yesterday and held an emergency meeting at 6pm last night.

Letters have been sent to parents advising them of the situation.

Two teachers and 28 of the boy's classmates are now in self-isolation.

Meanwhile an engineering student at the Manukau Institute of Technology was also confirmed with the virus but health authorities say they were not on campus while infected and posed no risk to fellow students.

Late Wednesday more than 100 pupils and staff at Mt Albert Grammar were placed in isolation after a senior pupil who went to school on Monday tested positive for Covid-19.

With the first confirmed case in Auckland's northern suburbs, those linked to the North Shore school are reeling after receiving the bombshell news last night.

A letter was sent to parents and staff just before 8pm from the Auckland Regional Public Health Service telling them a pupil at the school had tested positive.

The child was at school on Tuesday - the last day schools were open this week before closing to all but children of essential workers under alert level 3 - but had since gone into quarantine at home.

The child's family was also self-isolating.

The school is now closed to all staff and pupils, including those of essential workers, until at least Monday.

"There will be a great deal of concern in the school community, but the child did not have the symptoms while at school," the letter to parents read.

"This means there is a lower risk of the illness having been passed to other students."

Parents were asked to keep all children at home in isolation until they received a notification from ARPHS about the next steps.

"Everyone from the two schools and preschool should remain vigilant for the symptoms of Covid-19," said an ARPHS spokesperson.

Signs include a new or worsening cough, runny nose, fever, sore throat, difficulty breathing and temporary loss of smell.