Crews clean up after fire destroyed the Humane Society of Durham building on Dec 17. Police say 140 cats died in the fire. (Steven D'Souza/CBC)

Fire destroyed the Humane Society building in Oshawa early Wednesday, killing some 140 cats, three dogs and 60 hamsters, guinea pigs and other small pets, police said.

By the time fire crews arrived, they were only able to save 10 dogs, two cats and a rat. One of the surviving cats needed oxygen, three of the dogs were treated for chest congestion, while the rat was sent to be cared for in a foster home.

The rescued animals, according to police, were frightened and freezing.

"We got those animals that were able to be saved and put them in police cruisers, and kept them warm, and comforted them until the experts showed up from animal services," said Const. Dave Selby of Durham Regional Police.

Investigators are still trying to determine the cause of the fire, which started about 2:30 a.m. ET. Damage to the Oshawa building is estimated at $250,000. The shelter was already struggling to raise enough money to get a new facility to ease overcrowding.

"It's tragic that so many animals lost their lives so close to the holidays, where there was probably a good chance some of them would have found homes," said Ian McConachie, a spokesperson for the Toronto Humane Society.

Grief counsellors have been called in to help distraught shelter workers.

McConachie said the workers, volunteers and supporters of the Oshawa facility are distraught.

"It's always sad to lose an animal, to lose … 200 is just unthinkable," he said.

Alison Cross, a spokesperson for the Ontario Society for the Prevention of Cruelty to Animals, called the event "devastating."

"Their life's work is towards animals and helping animals and unfortunately, this tragic fire has destroyed that," she said.

"They spend their lives taking care of these animals and something like this is really heartbreaking to see and hear."

The Ontario SPCA, which is affiliated with the Oshawa facility, will assist with cleaning up, removing and properly disposing of the dead cats' bodies. It will also help the branch become operational again.

With files from the Canadian Press