A cat has become a national hero in Germany by saving the life of a newborn baby abandoned on the doorstep of a Cologne house in the middle of the night. The cat meowed loudly until someone woke up.

"The cat is a hero," Cologne police spokesperson Uwe Beier says. "Its loud meowing got the attention of the homeowner and saved the baby from suffering life-threatening hypothermia.

"The homeowner opened the door to see why the cat was making so much noise and discovered the newborn."

Beier says the baby was taken to hospital at about 5am local time on Thursday, when overnight temperatures fell down to zero degrees Celsius, and had suffered only mild hypothermia.

According to reports, there has been no indication as to who left the baby on the doorstep or what happened to the mother.