The sisters, who read in Chinese and English, follow a daily ritual of reading about six 500-word books each in the company of their mother, Lee Shui-ling.

'It's not a miracle that my three daughters finish about 2,000 books a year each, but a matter of persistence,' said Ms Lee. 'There are 365 days in a year, and if you read five to six 500-word books per day, [think] how many will you finish after a year.'

The latest certificates join others won by Yuen-kiu and Tze-kiu in the previous three years.

The sisters, who live in Sheung Shui with their homemaker mother and father, secondary school Chinese teacher Wong Kwok-leung, were taught how to read at the age of two, starting with Chinese characters before graduating to children's books at the age of three.

Every day the sisters and their mother all read for an hour while having tea after school. Middle sister Tze-kiu, who reads the most of the three, said while looking at the book she was in the middle of: 'I can finish such a book in five minutes.' Three minutes later, she put the book aside and chose another.

Mr Wong said much of the girls' interest in reading was due to his wife.

'Their mother devotes an enormous amount of time and energy to cultivating their reading habits. She chooses books for them and reads with them every day,' said Mr Wong, adding that his wife liked reading books on children's education.

Ms Lee admitted that she did not know at first how to foster her daughters' reading habits. 'I learned from their primary school's reading programme, which required all pupils to read at least one book a day,' she said. 'After reading and digesting the material, they were asked to answer some questions on the stories and then retell and rewrite them.

'The programme didn't force students to read five or six books a day, but my daughters love reading and read fast. I just created a good reading atmosphere for them and helped them form the reading habit.'

But with three hungry young readers in the family, there was no way the family could afford to buy so many books, let alone store them.

'I don't buy them many books, apart from some biographies of famous people when they are on sale,' said Ms Lee, who has, with her daughters, become an avid user of local libraries.

Yuen-kiu, the eldest Wong sister and a keen pianist, said she really enjoyed Beethoven's biography.

'I learned the spirit of persistence from him. He was a great musician who composed his most famous musical piece after he became deaf,' she said.

Tze-kiu's favourite books are the Harry Potter series because 'while there is no magic in the world, the author has created a magical world'.

Yuen-kiu likes Harry Potter, too. 'But my favourite book is written in Chinese and has the title of The Most Sincere Blessing. It's about a naughty boy who makes friends with a boy suffering from cancer and prays for him daily. There is a boy in my class nobody plays with, but I have made friends with him because I think it is selfish to isolate him. I have had the same experience as the character in the book,' said Yuen-kiu.

Man-kiu, the youngest, taking a peep at her two sisters from behind a raised picture book, said: 'I don't like those books my sisters read, but I like my sisters to tell the stories to me.'