Two teenage girls who suffered hypothermia during a weekend tramp in the Waitakere Ranges are off school today resting but are in good spirits, their principal says.

The Orewa College students, aged 15 and 16, were part of a group of 22 students and three teachers who became lost on Saturday while walking in the Waitakere Ranges for a silver Duke of Edinburgh expedition.

The girls were flown to Auckland City Hospital on Saturday night after the group set off an emergency locator beacon in the early evening after they were "cornered by a big swamp". They were released from hospital yesterday morning.

• Rescued teenage school trampers out of hospital


Orewa College principal Kate Shevland was confident in the school's procedures.

"The emergency beacon was set off when the teachers became concerned for two of the girls," she said.

"They're perfectly fine now, just a bit tired so haven't come to school today."

The school undertakes strict risk analysis before any outdoor education expedition or Duke of Edinburgh tramp, she said.

"The students and teachers all had the right gear, and they're at silver level so they'd had a bit of tramping experience.

"The area was just wetter than was expected ."

The school is holding a full debrief today to determine exactly what happened and if anything could be done differently in the future.

A Karekare resident yesterday told the Herald the group entered an area known as the Pararaha -- a swampy marshland about 40 minutes walk from the main Karekare Beach.

Karekare children visited there all the time, but for "city kids" it could have seemed a treacherous wilderness, the resident said.

"There's a bit of a swamp down there at the Pararaha. But for folk like ourselves it's actually pretty tame. Obviously, because it took a bit longer than they expected and it got a bit dark they freaked out a bit. But they were actually not very far from civilisation."

Meanwhile, in a second incident, a 17-year-old girl who was part of a six-person group tramping on the Twin Peak Track received hip and knee injuries on Saturday.

Search and rescue escorted the girl out of the Waitakere ranges on Sunday morning.