Japan's six-year-old Princess Aiko smiled nervously for the cameras as she arrived with her parents for her first day at Tokyo's exclusive Gakushuin elementary school on Thursday.

Aiko, who would be third in line for the throne if she wasn't a girl, was dressed in her school uniform of navy sailor suit with red neckerchief, and was accompanied by her parents, Crown Prince Naruhito and Crown Princess Masako.

She smiled after a word of encouragement from her mother, who was dressed in a white suit.

Aiko may be a royal but, like most Japanese elementary school pupils, she will walk to school each day, Kyodo news agency said.

The princess almost made it into the queue for the Japanese throne because of a shortage of male heirs.

But plans to change the law to allow an empress were shelved after Naruhito's younger brother fathered Prince Hisahito, the first boy born into the imperial family in four decades.

Under current law, if Aiko marries, she loses her royal status. Her aunt was transformed from Princess Sayako into Sayako Kuroda, an ordinary Tokyo housewife, after her marriage to an urban planner.