The measles virus is very contagious and can be serious. Photo: Supplied/ US CDC
Health authorities are urging anyone who went to a production at Kerikeri High School earlier this month to stay home to prevent the spread of measles.
Health New Zealand has added a school play called Monsters, at 7pm on 17 September, to its list of "locations of interest" - places where people may have been exposed to the virus.
Health New Zealand said anyone who attended the event but had not yet been contacted by public health staff should stay home and call Healthline urgently on 0800 611 116.
The official quarantine period was due to end on Wednesday, 1 October, but people who saw the play should stay alert for measles symptoms until at least 8 October.
The only other location of interest so far is Bay of Islands Hospital in Kawakawa, from 11.30pm on 19 September to 2.30am on 20 September, and again from 1.45pm to 7pm on 20 September.
Anyone at the hospital or adjoining GP clinic at those times should stay alert for symptoms until 11 October.
The alert does not apply to people staying in the inpatient ward.
Health New Zealand said the number of cases in the Bay of Islands remained at four, which was unchanged from Saturday.
National Public Health Service clinical director Susan Jack said all four cases were no longer infectious but it was not yet known if the virus had spread further.
She urged people to remain vigilant for the symptoms, which included a fever, cough, runny nose, sore eyes and a rash that started on the face and spread down the body.
Dr Jack said another case identified in Queenstown on Monday was unrelated to the Northland cases.
All were thought to be linked to overseas travel.
Health Minister Simeon Brown told RNZ on Tuesday morning work was underway to trace contacts of the Queenstown case.
He said more information was expected later today about possible locations of interest in the southern resort town.
Brown said his advice to Queenstown residents was the same he had given earlier to Northlanders, that immunisation is the best way of protecting children from measles.
Meanwhile, iwi health providers were continuing to ramp up their response in Northland.
Ngāti Hine Health Trust chief executive Tamati Shepherd-Wipiiti said immunisations were available from four clinics in Kawakawa, Moerewa and Whangārei, with mobile clinics due in Kerikeri, Waitangi and rural areas around Moerewa from Wednesday morning.
Shepherd-Wipiiti said about 40 people were immunised on Monday.
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