Tokyo (CNN) -- The image was horrific: A whimpering beagle, ribs showing through its fur, tethered to a post inside the no-go zone around the worst nuclear accident since Chernobyl.

The scene was captured by freelance journalists who drove through towns within a few kilometers of the Fukushima Daiichi nuclear power plant, and who left food for the animal. But animal rescue activists who have braved the exclusion zone around the plant say there many others like it.

"I understand the nuclear danger and everything, but they're just being left to starve to death, basically," said Isabella Gallaon-Aoki of Japan Earthquake Animal Rescue and Support.

Gallaon-Aoki and others like her have been slipping into the 20-km radius around Fukushima Daiichi to retrieve pets and feed livestock left behind when their owners were forced to evacuate. Pet owners have sent her group their addresses, accompanied by pleas to rescue their animals, left behind when they fled for what was supposed to be a short time.

A month later, the volunteers are putting their long-term health on the line, putting on protective gear and entering the 20-km radius around the plant that was declared off-limits in the early days of the crisis. Hiroko Ito's 5-year-old Shiba, Non, is among those rescued by Gallaon-Aoki's group. Ito said she left food for the dog, but didn't expect to be gone a month.

"We tried to save him, but we couldn't get in," Ito said.

Radiation levels recorded by photographers Shuji Ogawa and Naomi Toyoda were not high enough to cause immediate illness, but would pose potential health risks with prolonged exposure. Gallaon-Aoki said she knows the risks, "but I feel personally that the risk that there is is worth taking for what I can achieve by doing so."

From the prime minister's office to town halls, Japanese authorities told CNN they have no provisions for dealing with animals when their owners are ordered to clear out -- orders that have been expanded to other towns around the crippled power plant, which has been emitting radioactive particles since the March 11 earthquake and tsunami that knocked out its coolant systems.

Gallaon-Aoki called that "unforgivable."

"I understand they have a huge problem as far as people are concerned. They are dealing with a lot," she said. "But, I mean, there are people and groups who would be willing to help, and surely they could kind of set some sort of well-coordinated effort."

The fate of the tethered beagle Ogawa and Toyoda captured on video was not known early Thursday.