Police are unsure of the motives for the attack.

His father has a gambling habit, although he denies being in debt to loansharks.

Speaking at the Yan Chai Hospital yesterday, Ho-yin's father said: 'The first thing he said when he woke up was: 'Where's grandma?' He is getting better. And his emotions are calming down.'

Doctors at the children's ward said Ho-yin's condition had improved from serious to stable. Three detectives from the New Territories South Regional Crime Unit visited the boy yesterday afternoon and said he was in good spirits.

They declined to say if they had taken Ho-yin's statement.

Police are believed to have talked to the staff of S.K.H. Chu Oi Primary School and the social services centre where he had his summer tutorial classes.

They have also visited the estate's security control room. Both the school and the centre are next to the grandma's flat where Ho-yin lives in Block 5 of the estate.

The seven-year-old has a passion for sketching, but his injuries may prevent him pursuing his hobby. Tsuen Wan District Councillor Wong Ka-wa, who rushed to help Ho-yin after the attack, said the boy was right-handed.

It is not yet known whether his arm will be permanently damaged.

Mr Wong said: 'Kids love drawing anyway, and he has bought several sketch books.'

The owner of a stationery shop located near Ho-yin's block said in tears yesterday that the boy was a regular customer, who was an 'attractive, polite and extremely smart kid'.

The woman, who identified herself as Mrs Hui, said she wept when she heard about the attack because she recognised Ho-yin as the boy who showed up at her shop several times this summer to buy A4-size sketch books.

'He always came in with his grandmother and both were very polite,' she said. 'He came again with his grandmother a few days before the attack and bought a sketch book and a toy, which I assumed was a gift for someone else.

'The bill was more than $30 and the grandmother gave me a $100 note. I asked Ho-yin if he knew how much I had to give to his grandmother. He gave me a quick, correct answer and I praised him.

'Then his grandmother smiled and said, 'Yes, he is good at maths,'' Mrs Hui said, fighting back tears.

'He must love drawing because he bought so many sketch books,' she said, adding that she has given some colouring pens to Mr Wong to give to Ho-yin.

Mrs Hui said she wanted to visit Ho-yin in hospital but did not want to disturb him.

Commissioner of Police Dick Lee Ming-kwai said yesterday the case was extremely rare but he was confident it would be solved soon.