A baby is battling for his life at a Pakistan hospital after being born with a rare genetic condition that left him with six legs, hospital officials said.

According to AFP, the infant was born to the wife of an X-ray technician a week ago and is believed to be one of parasitic twins.

"It is not one baby actually. They are two, one of them is premature," Jamal Raza, the director of National Institute of the Child Health in Karachi, told reporters.

Doctors at the institute are fighting to save the newborn, who remains in an intensive care unit ward.

Raza said the doctors were planning to operate on the boy and were considering asking for help from foreign experts.

The rare disease is believed to afflict just one in a million babies.

"The doctors are examining the infant to plan for necessary treatment to save the baby's life and ensure he lives a normal life," a statement from the provincial health department said.

The baby's father Imran Shaikh who lives around 450 kilometres from the city of Karachi said he was grateful his son was being treated and that he was too poor to afford the treatment.