A premature baby who survived hours in a morgue refrigerator after being mistakenly declared dead has suffered a cardiac arrest and is in critical condition, Argentine doctors said Friday.

Luz Milagros "had a that required advanced resuscitation. She showed signs of pulmonary and ," said Diana Vesco, chief of at the Perrando Hospital in northeastern Argentina.

The newborn's condition worsened on Thursday with an infection, for which she was given antibiotics, Vesco told reporters.

Officials had signed her death certificate after she was born prematurely on April 3 at six months gestation weighing only 800 grams (1.76 pounds).

But the baby's miraculous survival prompted her parents to rename her Luz Milagros -- the Spanish words for light and miracles.

She had survived some 12 hours in a coffin inside a morgue refrigerator, and was only determined to be alive after her mother insisted on seeing the body.

"At night, I went with my husband to where the little box was. A man pried it open. I suddenly heard a whimper. She was all covered up and full of something that looked like frost," Analia Bouter told local media.

An investigation has been launched to determine who was responsible for mistakenly pronouncing the baby dead.

The hospital's director Jose Luis Meirino said the baby was likely able to survive because she "suffered , during which the body went into hibernation and stopped its vital signs."