Princess Kiko, the wife of Prince Akishino, will give birth by Caesarean section to her third child on Wednesday morning.
The royal birth has attracted even more attention than usual as people speculate over whether the Imperial family will see the first birth of a possible heir to the throne in nearly 41 years.
No boys have been born into the Imperial Family since the birth of Prince Akishino in November 1965. A young prince has long been awaited because by law only males who have emperors on their father's side can ascend the throne.