Beijing (CNN) Police rescued a baby boy buried alive in a shallow, unmarked grave on a hillside in southern China's Guangxi province, according to the country's state media.

Chinese news reports say the baby was believed to have been left alone in the wilderness for as long as 10 days, but the details remain unclear.

The boy's family decided to abandon him because he was born with a cleft lip and a congenital defect, according to a Xinhua news agency report . In China, thousands of infants with birth defects are abandoned every year.

CNN could not verify the details reported in Chinese media because police and the Civil Affairs Bureau, which is taking care of the baby, declined to give more information to foreign media.

Police: Baby left to die

The boy was born on April 20 and discharged from the hospital four days later after receiving treatment for a high fever, according to Tiandong County People's Hospital.

The baby arrived at the hospital in critical condition.

"Normal parents ask the hospital to provide a birth certificate and arrange for medical insurance, but this family didn't want a birth certificate and left immediately after paying the bill," Wu Weili, deputy director of pediatrics at the hospital, told Xinhua.

"We do not know what exactly happened during the period of time when the baby was discharged from the hospital on April 24, and when he was admitted to the hospital again on May 4."

On April 24, the family -- including the infant's grandmothers -- allegedly hired a man for $290 to get rid of the baby, according to Xinhua.

That day, the hired man left the newborn to die in a cardboard box in the wilderness. Two days later, believing the baby to be dead, he buried him, according to Xinhua.

Later, a woman who was picking herbs on a hillside heard a wail. With the help of a few villagers, police rescued the baby and sent him to the hospital.

Wu said the baby was in critical condition -- coughing up mud, his whole body covered in scratches and bruises -- when he arrived at the hospital.

The baby was discovered in a cardboard box placed in a shallow grave.

The baby weighed 7.8 pounds when he was born. By the time he was rescued, he weighed only 5.9 pounds.

"It really is incredible," Wu told Xinhua of the infant's survival.

Parents want baby back

Five people -- including the baby's parents, both of his grandmothers and the man they hired to dispose of the newborn -- have been arrested for attempted murder. His parents were released on bail and they are now trying to regain custody of the boy.

They wrote a letter of apology, promising not to hurt him, Xinhua reported.

"We worry that the baby's parents may hurt him again," Zhou Liying, head of the county's Civil Affairs Bureau, told Xinhua. "Even though they will not, this tragedy may haunt the family and affect the boy's mental health."

The baby is being nursed back to health and doctors say he can be discharged later this week. Local government officials say the baby would most likely be put into the care of social services.

His parents and grandfather visited the hospital to see the baby for the first time on Tuesday.