Seventy-one children at a Quebec daycare center were rushed to hospital Tuesday with carbon monoxide poisoning, authorities in Canada said.
Workers at the daycare in Saint-Eustache, 45 kilometers (30 miles) northwest of Montreal, called for help after they and several of the children began vomiting and complaining of violent headaches.
Symptoms in only a few of the children were initially dismissed because daycare staff believed they could be signs of flu.
But they quickly realized something was seriously wrong when they too began to fall ill, Quebec government minister Francine Charbonneau told a press conference.
"Five children developed symptoms a bit more severe than the others" and were treated in hospital while the others remained under observation, she said.
Carbon monoxide can cause headaches, nausea and fatigue. Prolonged exposure can be fatal.