TOKYO (AFP, Yomiuri Shimbun/Asia News Network) - Japan's panda population grew by two, a zoo announced Wednesday, with the birth of twin cubs Tuesday night.

The pair came into the world weighing less than 200 grammes each, a spokesman for Wakayama Adventure World in western Japan said.

The birth of the two cubs takes to seven the number of pandas at the zoo, which has an active breeding programme for the creatures that have a notoriously low reproductive rate.

At just 21 and 22 centimetres the tiny youngsters have a long way to go before they are the size of their mother, 14-year-old Rauhin.

This is the third time Rauhin has given to birth to twins, after her previous deliveries in 2008 and 2010. The Tuesday delivery made her a mother of seven and raised the total number of pandas born at the leisure park to 15 - a record high at a facility outside China.

Kyodo News reported that the latest twins have made a good start, with the first-born beginning to breast feed soon after its birth.

The zoo is yet to name the cubs and has not decided when to place them on public display.