Thirty one boys and teachers from a Hawke's Bay boarding school have been sent home or isolated after some members of a group had flu-like symptoms after returning from North America this week.

Three of the group, which included four teachers and 27 students from Lindisfarne College, developed flu-like symptoms after returning on Tuesday, the Hawke's Bay District Health Board reported.

Medical officer of health Caroline McElnay said moves to isolate all of them was precautionary.

Dr McElnay said samples had been taken from the boys affected and they had been offered Tamiflu, as had the rest of the group.

Some extra samples were also taken last night.

College rector Grant Lander said the situation had forced the school to postpone its gala opening, as the boys were all in the school's orchestra, but advice from health officials needed to be followed.

A small number of the boys who were boarders and unable to go home were being kept in isolation at the school.

Dr McElnay said results from the samples taken were expected over the next few days.

The Ministry of Health has confirmed three people have contracted the virus, while another 13 were being treated as confirmed cases. All were in the Auckland area.

In Mexico, where the virus was first identified, over 160 are reported to have died after either contracting swine flu, or having been suspected of contracting it.