The Hong Kong Bird Watching Society on Monday said a rare scaly-sided merganser has been spotted for the first time in Hong Kong, describing its visit here as "very special".

The duck, which has feathers that resemble fish scales, normally breeds in northeast China and flies to provinces including Jiangxi and Hunan in the winter.

This year, one has been seen at a reservoir in the New Territories.

The society's director, Yu Yat-tung, said he is pleased and excited to see the bird making an appearance here, because there's a high chance the scaly-sided merganser will become extinct in the future.

"It's somehow normal for a migratory bird to come to the south, but Hong Kong is not their normal winter ground, so that is why we say this is very special," he said.

But Yu said the duck won't stay in Hong Kong for long.

"The bird could leave very soon because the weather now is getting warmer, and then it will start its northward migration to go back to the breeding site."

Yu said the bird is in good health, apart from some injuries to its bill. He urged people to keep away from the duck and to only observe it through binoculars.