A BABY girl, thought to be less that 12 hours old, was abandoned in the foyer of a block of units in Mortdale, in southern Sydney, yesterday afternoon.

Residents of the building, two blocks from the railway station, found the newborn at 4.30pm and cared for her until police arrived.

An ambulance took the girl, reported to be in good health, to St George Hospital.

One resident said the baby's umbilical cord was still attached.

"It's shocking to dump a baby when so many people want to adopt," she said. "You just don't drop it on a cold cement floor."

Another resident said whoever left the baby must have walked in off the street. "Police have been through the whole place trying to find information about the baby.

"It was just dumped in the foyer of the block. Whoever [abandoned the baby] came in through the main front entrance because we were out the back chatting."

Police are concerned about the mother's welfare.

"Police canvassed the area without result," a police media spokeswoman said. They are appealing for her to come forward.

Alex Tibbitts