It started with just one young swimmer getting in trouble. Other school pupils went to help - and within minutes 11 teenagers from the same school group were being dragged out to sea in a vicious rip.

The Lowe Corporation rescue helicopter took two students to hospital after being called to Pourerere Beach in Hawke's Bay on Friday afternoon. Another nine students were taken to hospital by ambulance.

Yesterday, the principal of Central Hawke's Bay College in the inland town of Waipukurau insisted he was happy with the safety precautions taken on the school trip. Dawid de Villiers spoke with relief about the students' escape from what could have been a tragedy.

There was an "overkill" of staff at the beach at the time, he said, and the students had received a safety briefing before going into the water. "But I know that when it comes to the seas and the ocean there are other factors at play."

The 11 teens were discharged without injury in the evening, a Hawke's Bay District Health Board spokeswoman said.

The students, one aged 17 and the others all aged 13 or 14, were part of a group of 150 students visiting the beach, about 50km southeast of Napier, during an annual peer support day.

At midday, several students decided to go for a swim and senior students were placed in the water to act as safety barriers. The younger year 9 students were meant to be supported by the senior students and about 14 parents. Instead, one of the older students was among those caught in the rip.

"The students were in the water about 10 minutes before the first one got into trouble - then the rip moved them off," said de Villiers.

Some had to be pulled from the water by teachers and other students; others managed to escape the rip themselves.

They were shivering when they got back to the beach, and one student was coughing after swallowing water.

"We covered them up and kept them warm. I wasn't sure if it was hypothermia or shock," de Villiers said.

De Villiers said he'd talked with all of the families of the students involved.

De Villiers took up the principal role at the school four weeks ago after moving from Dannevirke High School where he was deputy principal. That college made the front page last year when the Herald on Sunday revealed it had employed teacher Natasha Miller and her partner Hayden Macdonald.

Miller had previously resigned from a nearby school when it was discovered she was in a relationship with Macdonald, who was then aged 16 and a student.