More than 600 Hawaii shelter cats and dogs are en route to the U.S. mainland to seek their forever homes in one of the largest pet rescue flights in history organized by national nonprofits, Greater Good Charities and Wings of Rescue.

The mission, dubbed “Paws Across the Pacific,” planned stops on Kauai, Oahu, Maui and Hawaii island in a chartered, Hercules C-130 plane, in coordination with the Hawaii Emergency Management Agency and Hawaii Veterinary Medical Association.

It made a second stop in Honolulu Wednesday evening to pick up shelter cats and dogs from the Hawaiian Humane Society.

The Hawaii dogs and cats are being flown to shelters in Washington state, Oregon, Idaho, and Montana, where they are expected to be adopted into forever homes.

“Pet shelters in Hawaii are in a COVID-19 crisis,” said Liz Baker, CEO of Greater Good Charities, in a news release. “Normal operations have been affected by months of shutdown, economic downturn, limited hours, and routine flights to mainland halted, The Paws Across the Pacific flight is urgently needed to make space in Hawaii’s shelters for at-risk pets who otherwise wouldn’t be able to receive necessary care to survive.”

>> PHOTOS: Shelter animals prepare to leave Honolulu

Hawaii shelters that are participating include the Kauai Humane Society, Hawaiian Humane Society, Lanai Cat Sanctuary, Hawaii Island Humane Society, Maui Humane Society and Aloha ‘Ilio Rescue.

By unofficial estimates, there will be more cats than dogs on the plane.

The Hawaiian Humane Society is sending, at last count, 97 cats, and six dogs, according to spokesman Daniel Roselle. The animals boarding the flight include a mix of kittens from 2 months to cats 3 years old, and dogs from 7 months to 5 years old.

“The vast majority of the animals we are sending over already have homes lined up, or are going to organizations with high demand for pets to adopt,” said Roselle in an email. “It might surprise people to know that there are very few really challenging cases for adoptions. The animal loving community members on Oahu have really big hearts. We adopt out pets with amputations, senior dogs and cats, blind pets, cats with FIV [feline immunodeficiency virus].”

Roselle said the primary consideration for the pets selected were whether they were healthy and strong enough to make the trans-Pacific flight. Many dogs and cats still remain available for adoption at the Hawaiian Humane Society, he said.

Maui Humane Society will be sending 87 cats and dogs — mostly cats — on the plane, according to spokeswoman Jenny Miller.

Although animals adoptions have been in demand during the pandemic, more kittens were also born this year because the shelter’s low-cost spay and neuter clinic had to close down for several weeks. As a result, the nonprofit had to reach out and ask for fosters for cats, and a total of 60 that were being fostered will be on the flight.

The pandemic also put a temporary stop since March to Maui Humane Society’s “Wings of Aloha” program, which usually sends 50 to 60 animals per month to mainland shelters for a better chance of adoption, due to the lack of direct flights.

This flight was an opportunity to alleviate crowding at the Maui shelter, said Miller. She said she heard some places in the Pacific Northwest have a deficit of animals available for adoption, and a wait list for the adoption of cats.

One of the dogs going on the flight has already been adopted by a mainland resident who recently visited Maui.

“This is a huge help,” she said. “We’re so grateful.”

Lanai Cat Sanctuary is sending 55 of its feline residents via Kamaka Air Cargo, which donated a flight from Lanai to Maui to meet the plane.

“We are beyond grateful to be a part of this historic rescue,” said Keoni Vaughn, executive director of the Lanai Cat Sanctuary. “With 55 of our cats finding homes, we’ll have the capacity to rescue 55 more at-risk cats on Lanai who otherwise wouldn’t be able to receive the necessary care to survive.”

While all 690 of the sanctuary’s cats are welcome to stay forever, he would prefer them to have warm laps and homes.

The plane is scheduled to arrive at Seattle’s Boeing Field on Thursday, where pet shelters and rescue groups will pick most of them up, and about 120 will continue on to Walla Walla and Coeur d’Alene.

Mainland shelter partners participating include: PAWS, The NOAH Center, Seattle Humane, the Humane Society of Skagit Valley, Kitsap Humane, Oregon Humane, Southwest Washington Humane, Kootenai Humane Society, Seattle Area Feline Rescue (SAFR), Tracs, Spokanimal, Blue Mountain Humane Society, and Embrace a Discarded Pet Society.