Los Angeles, California - Hundreds of dogs and cats were rescued Friday from an animal shelter north of Los Angeles in potentially the largest such operation in US history, officials said.

The animals were found living in poor conditions at a facility in Lake Hughes, 70 miles north of Los Angeles. US media identified the shelter as Rock N Pawz.

More than 70 workers with the Los Angeles County Department of Animal Care and Control were involved in the rescue, along with members of animal welfare organizations.

The organization originally reported 700 animals were rescued during the operation, later modifying the total down to 316 – 250 dogs and 66 cats – after performing an in-house count.

The animals had been housed in cages with sporadic feeding and no water as the region was experiencing a major heat wave, said Marcia Mayeda, the department director.

"She had been taking in more animals than she could properly care for," Mayeda said at a press conference at the scene, referring to the shelter owner.

"This resulted in a very negligent and dangerous situation for the animals, who needed to be removed for their safety."

The animals in serious condition were taken to veterinary centers, while others went to shelters for monitoring and treatment.