BEIJING, May 15 (Reuters) The world's only koala twins, born seven months ago and raised in a south China zoo, have passed a critical development stage and now have a good chance of surviving, a zoo official said.

The koalas, born in October at Xiangjiang wildlife park in Guangzhou, capital of southern Guangdong province, are one of only two pairs of captive-born twins ever recorded, local media and zoo officials said yesterday.

The other pair was born at an Australian university laboratory in 1960.

''They are about 300 grams each, just like the size of a small human fist,'' a Xiangjiang zoo official told Reuters.

''(They are) a little bit smaller in size than average koalas their age, but they are growing well and are healthy,'' he told Reuters in a telephone interview.

Animal experts have said that chances of both twins surviving are small, but the now 7-month-old babies had successfully passed their most dangerous period.

''We had 24-hour supervision and care for the twins a month before they came out of their mother's pouch, which was the most dangerous and crucial time for their survival,'' he said.

''All our workers at the zoo love them very much, and we will try everything we can to help them grow,'' he added.

The gender of the baby koalas, temporarily called ''Michelle'' and ''Amanda'', was still unclear, but would be known after testing when they are a bit older, the official said.

''There will also be a naming campaign for them in the summer, as they need Chinese names,'' he said.

The mother of the twins, known as Tao Tao in Chinese, was one of six koalas given to the Xiangjiang zoo by an Australian wildlife sanctuary last year.

REUTERS SZ HS0930