The number of people confirmed to have caught measles in Christchurch has risen to eight, up from four on Monday.
Canterbury medical officer of health Ramon Pink says one of the cases is a person in their 20s, while the others are students from Christchurch Boys High School.
One of them has been admitted to hospital.
Dr Pink says another nine people probably have the virus.
Principal Trevor McIntyre says a school trip involving 22 teachers and pupils to New Caledonia has been postponed so as not to spread the virus.