A woman is missing after several hikers are stranded in the Grand Canyon due to a flash flood.

Flooding reached Havasu Creek around 1:30 p.m. local time on Thursday, the National Park Service said in a news release, stranding hikers above and below the striking, bright blue Beaver Falls.

Rescue efforts began immediately, park officials said, and a first flight to assist stranded hikers took off before 3 p.m.

Chenoa Nickerson, 33, was swept into the creek by the flood, park officials said. Havasu Creek connects to the Colorado River. Nickerson is believed to have fallen into the creek about a half-mile from where it empties into the 1,450-mile-long river, park officials said.

According to CBS affiliate AZFamily, Nickerson was hiking with her husband and was not wearing a life jacket. Her husband was rescued by rafters.

Nickerson is the only hiker missing after the rescue. Search and rescue efforts are ongoing, the National Park Service said. Anyone with information about Nickerson is asked to contact park authorities.

Her sister, Tamara Morales, said on social media Saturday that Nickerson was still missing and praised National Park Service rescue crews for “navigating incredibly dangerous terrain with extremely limited communications and leaving no stone unturned.”

“We are deeply grateful to you and fully recognize that you are currently questioning the impossible,” Morales said on Facebook.

A missing person report described Nickerson as a 5’8″ (1.73 m) tall, 180 lb (86 kg) woman with brown hair, blue eyes and tattoos.

The Havasupai Tribe, which provides hikers access to the Supai area where the falls are located, posted on social media that the area would be closed until Sunday. The tribe said it was still working to evacuate hikers affected by the flooding.