Japan has finally launched formal discussions on how to secure a stable succession to the chrysanthemum throne amid a shrinking number of heirs, with options including allowing women or emperors from the maternal line to reign.

A six-member government panel held its first meeting on March 23, with its chairman, Atsushi Seike, a former Keio University president, vowing to hold "careful discussions" without haste as the government seeks to secure a stable future for the world's oldest hereditary monarchy.

But the clock is ticking for the family, which is now left with just three male heirs, as women marrying commoners have to abandon their imperial status under current rules.