The mother of a newborn baby was shot dead outside a US maternity centre by a nurse who then drove off with the child.

The healthy three-day-old boy was found about six hours after the killing in Montgomery County, Texas. The baby was reunited with his father.

Police said a woman had been detained, although no charges had been filed.

The boy's mother, 28-year-old Kayla Marie Golden, was leaving a check-up with her son when she argued with a woman in a car parked next to her truck.

Witnesses said the woman repeatedly shot Ms Golden, took the child and sped away, hitting the dying mother as she tried to reach into the car. They reported hearing as many as seven gunshots and said a man was also in the Lexus.

Joshua Jesson said he was in the clinic with his girlfriend when he heard gunshots.

He said he saw the Lexus next to the truck, then later looked back and saw the car was gone and a woman was lying there.

"I thought she just passed out. Then somebody ran in here and said, 'Somebody got shot'," he said.