A United Nations convoy has visited 17 stranded B.C. Interior high school students and their chaperones in Haiti and determined that the best way to get the group out is via a military helicopter, a school official said Friday.

But it's unclear when they will be evacuated.

Patricia Dooley, superintendent of the Kootenay Lake School District, told reporters she learned of the U.N. visit during a phone call from B.C. Solicitor General Kash Heed late Friday morning.

Defence Minister Peter MacKay told CTV News Friday that the federal government is working on the logistics of getting the student group out, perhaps to the Canadian embassy first, then onto an aircraft to Canada.

"We are very aware of the urgency," he said.

Meanwhile, the 17 students from Mount Sentinel Secondary in South Slocan, B.C., and their chaperones sent out a second group email Friday indicating that they are experiencing aftershocks about every 90 minutes.

"We started the day with a larger tremor at 4 a.m. It shook our shelter and sent the kids running," wrote Jim Reimer, pastor of Kootenay Christian Fellowship and one of the group's chaperones.

For safety reasons, the group has been sleeping outdoors under a tin roof, Reimer wrote. The students are sleeping in a row on plywood.

Contrary to what U.N. staff had advised in an earlier visit, the student group on Friday ventured outside the mission compound where they are staying.

The students were so moved by what they saw, they put together $2,500 to buy 4,000 pounds of rice that they distributed to local families, Reimer said.

"One of the students said, 'each day is getting better for me, this experience has changed my life forever,'" Reimer wrote.

Reimer said the group is concerned about running out of food for themselves after $10,000 was stolen from the compound.

In an email on Thursday, Reimer said one of the adult chaperones in the group was believed to have a broken rib and in a lot of pain. There was no update on her condition Friday.

The student group arrived in Haiti 45 minutes before Tuesday's earthquake struck. They were scheduled to be in Haiti for two weeks working on a variety of service projects, including constructing a well and doing work on a goat farm.

Dooley, the school superintendent, said Friday that she was struck by the students' generosity.

But she said she also felt nervous hearing that they had ventured outside the compound.

"We won't rest," she said, "until the kids are on Canadian soil."