Japan's emperor diagnosed with pneumonia

Emperor Akihito has been diagnosed with mild bronchial pneumonia (GETTY IMAGES)

Emperor Akihito has been diagnosed with mild bronchial pneumonia and remains in hospital for a 12th day, Japan's royal household said.

The Imperial Household Agency said in a statement today that the emperor is responding to antibiotics.

His fever climbed to near 39C but is now falling.

The emperor, 77, developed a fever two weeks ago and was admitted into University of Tokyo Hospital on November 6.

The emperor ascended the throne after his father Hirohito died in 1989.

His wife, Empress Michiko, remarked last month that staying healthy is an uphill battle for the popular royal couple.

Akihito has been on hormone therapy since prostate surgery eight years ago. He also takes medication for his arteries.