Vets have called the dog…Pocket.

When an alleged drug dealer was arrested in Lawrence, Massachusetts, officers made a rather remarkable discovery in one of his pockets.

A tiny puppy!

The American pit bull terrier, thought to be around 3 weeks old, was handed to a local rescue centre before being treated by vets at the BluePearl Veterinary Partners in Waltham.

BluePearl Veterinary Partners / Via bluepearlvet.com

The veterinary group said the puppy was extremely unwell when it first arrived.

It was vomiting and had diarrhoea, "potentially life-threatening conditions for the tiny pup, separated from her mother", they said.

"I was actually shocked at how tiny she was – she didn't have any teeth and was just like a tiny loaf,” Alexis Bywater, the puppy's foster mother, told 7 News.

Vets said the dog's initial prognosis was grim, but after a day of supportive care things began to improve.

The puppy is now expected to make a full recovery and could be discharged today.

BluePearl Veterinary Partners / Via bluepearlvet.com

The female puppy has been given the name Pocket because of where she was found.

Once Pocket is old enough and medically fit, she will be put up for adoption. Those interested should visit pittieloverescue.org.

BluePearl Veterinary Partners / Via bluepearlvet.com