DENVER -- A toddler fell to the bottom of a narrow, 12-foot construction hole yesterday afternoon, and firefighters worked into the night to rescue him.

Firemen broke through a layer of hard clay shortly after 9 p.m. Mountain time as they dug a parallel shaft to rescue 20-month-old Kevin Davis from the hole at his family's home in southeast Denver.

The shaft is about 18-inches wide at the top and was to be filled with reinforced concrete for a remodeling project.

The boy's parents, Tom and Lisa Davis, were talking to Kevin, trying to soothe him during the rescue effort. Oxygen was being pumped into the shaft.

Denver policeman W.C. Hoffman said the threat of a cave-in diminished after diggers finally broke through the clay that had slowed digging efforts throughout the night.

"We're letting him sleep for now. He's been sleeping off and on. We've had to play around with the oxygen {tube to the boy} because he doesn't like the sound {hissing} of the oxygen. Every time he wakes up he cries," Hoffman said.

Rescuers were ready to grab the child with a snare on the end of a pole should a cave-in threaten the little boy, who is too young to grasp a rope that could be lowered to him. Hoffman said rescuers preferred not to use the snare because it would break any limb they might pull on.