CONCORD -- A baby rescued from a swimming pool attempted to breathe on his own as he was taken away in an ambulance Sunday and was in stable condition at a hospital Monday, authorities said.

Relatives were performing CPR on the unresponsive 1-year-old boy when Concord police arrived at a residence in the 1700 block of Ducker Court around 6:15 p.m. Sunday night, Lt. David Hughes said. Officers took over the lifesaving efforts, then were relieved by paramedics who arrived a short time later.

An air ambulance was called to the scene, but medical personnel opted to take the boy to John Muir Medical Center in Walnut Creek when he attempted to breathe by himself, Contra Costa Fire Protection District spokesman Robert Marshall said. He was listed in critical condition Sunday night before being upgraded to stable condition.

"He was in fairly bad shape," Marshall said, but added that the boy attempting to breathe on his own was an encouraging development. "That's always a really good sign."

When asked if it was too early to assume the boy would survive, Marshall said should such speculation would be premature but added that the baby's recovery seemed to be pointed in the right direction.

He also said the CPR by the family was critical.

"Any CPR helps," he said. "Anytime you can do early CPR on someone, we recommend you do that."

Police are investigating how the baby got into the pool. They did not say whether a gate or barrier surrounded the pool or disclose any other details about the investigation.

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.