The Kalalau Trail at Napali Coast State Wilderness Park on Kauai in Hawaii is shut down after dozens of hikers and campers fell ill from the norovirus.

The Hawaii Department of Land and Natural Resources first planned to shut down the trail for a week, then extended the closure to Sept. 19. The Kalalau area can host 80 campers, and several left before Wednesday, one by hiking and others by boat, after getting sick, DLNR officials wrote in a release.

“This is a very concerning and rare occurrence, magnified by the extreme remote nature of the Kalalau Valley,” DLNR Division of State Parks Administrator Curt Cottrell said.

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Department officials on Friday confirmed that at least 37 hikers and campers had contracted norovirus, which causes vomiting, diarrhea, abdominal cramps and fever.

DLNR officials flew into the park this week to tell remaining campers they had to leave. Two visitors to the area were written a citation for hiking beyond Hanakapiai Beach without a permit.

“We figure camping, people get sick. Maybe they drank the water. People get sick, but when they start going through the protocols of shutting down the park, actually this is something a little more serious,” Forrest Liss, who hiked in Tuesday and left after hearing about the mass illness, said in a DLNR release.

The camping comfort station in Kalalau has been cleaned and disinfected, though persistent squatters in the state park present an issue in fully clearing out the norovirus.

Anyone found traveling into or found at the closed portion of the park during the closure period will be written a citation or arrested, DLNR officials said.