All pupils and staff at a Co Kerry school are to be tested for Covid-19, with all children asked to restrict their movements until 30 December, according to a letter sent to parents by the Health Service Executive.
Seventeen cases at Scoil Mhuire in Killorglin, a mixed primary school with 386 pupils, have been recorded "and contact tracing is ongoing," the letter from HSE South's Department of Public Health states.
It is one of the largest outbreaks in a school to date.
"In the Irish experience with Covid-19 thus far, it has been uncommon to see an outbreak of this scale among a school population," the letter says.
School management is implementing coronavirus control measures and cases and close contacts have been isolating.
"Following further review today, based on current evidence, the decision has been taken to extend testing to the remainder of the school population, (children and staff)," the letter adds.
Any child not previously identified as a case or a close contact is now advised to restrict their movements until Wednesday 30 December," it advises.
The children are being referred for two tests, a number of days apart, by the HSE.
Restricted movement means "the child does not go to school," according to the letter.
They are also asked to stay away from older people and not have visitors in homes.
Meanwhile, pupils in a junior infants class in Tralee have been asked to remain at home until after Christmas.