The premature girl who "still had fresh placenta" and was "freshly born" was found at Bear Creek in the city of Katy just west of Houston, Texas, on Saturday, said Sergeant Juan Garcia of the Harris County Sheriff's Department.

CCTV footage shows the suspect - described as having a slim build - slowly walking to a bridge with the child.

After placing down the baby, the man then walks away slowly before sprinting out of sight.

Temperatures in the area over the weekend reached as high as 35C (95F), according to the National Weather Agency so the little girl would have had little chance of survival.

Fortunately, a young couple walking with their own child and dogs spotted the newborn and called the police.

Daniela Fedele told NBC News affiliate KPRC 2: "We were coming back from our walk this morning, heading home because it was hot.

"When I went ahead and looked closer, that's when I noticed a little baby with like her two feet moving.

"I think it was like, am I seeing this, right? Like, are my eyes really seeing a baby here?"

Her husband, Luis Marin, added: "I hold it. The baby opens their eyes to me, looked at me.

"We make eye contact. And I'm like, how can somebody just do this?"

Sgt Garcia described the couple as a "blessing" and said they noticed the suspect walking away before rescuing the child.

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Harris County Sheriff Ed Gonzalez added that the as yet unnamed baby was in good condition and that officers were hunting the man who had abandoned her.

Neither he, nor the child's mother have yet been identified.