Image copyright Keio University Hospital Image caption The baby at the age of five days...

A baby boy who weighed just 268g (9.45oz) at birth has been released from hospital in Japan, and is believed to be the smallest boy in the world to have been successfully treated.

The baby was born by emergency C-section in August, and was so small he could fit into a pair of cupped hands.

The infant was nurtured in intensive care until he was released last week, two months after his due date.

He had grown to a weight of 3.2kg, and is now feeding normally.

Born at 24 weeks, the tiny boy spent five months in hospital.

"I can only say I'm happy that he has grown this big because honestly, I wasn't sure he could survive," the boy's mother said, according to Tokyo's Keio University Hospital.

Doctor Takeshi Arimitsu, who treated the extraordinary baby, told the BBC he was the smallest infant born (on record) to be discharged from a hospital, according to a database of the world's littlest babies held by the University of Iowa.

He said he wanted to show that "there is a possibility that babies will be able to leave the hospital in good health, even though they are born small".

Image copyright Keio University Hospital Image caption ... and weighing a healthy 3.2kg - twelve times his birth weight - just before he left hospital

The previous record-holder was a boy born in Germany, weighing 274g. The smallest surviving baby girl in that same database was also born in Germany, in 2015, and reportedly weighed 252g.

Keio University Hospital said the survival rate of babies born weighing less than a kilogram is about 90% in Japan. But for those born under 300g, that falls to around 50%.

Among the very smallest babies, the survival rate is much lower for boys than girls. Medical experts are unsure why, though some believe it could be linked to the slower development of male babies' lungs.