It brought the total number of kidney stone cases affecting children born in Hong Kong to four, said the Center for Health Protection of the Department of Health.

The HKSAR government said in a press release that one of the newly confirmed cases involved a 29-month-old boy who was born in Hong Kong but lives in the mainland. He used to consume milk products contaminated with melamine.

The boy was taken to a Hong Kong hospital for examination on Monday and was diagnosed of renal stone. He was now under treatment and in stable condition.

The fourth case involved a nine-year-old boy who was born in Hong Kong but has been living in the mainland since he was two. He consumed melamine tainted milk products in the past four years and has no symptoms of renal problems. He was taken to a private hospital in Hong Kong for examination on Saturday and was found to have a kidney stone. He was admitted for treatment thereafter and, having been discharged, was stable now.

Milk products contaminated with melamine, a chemical substance usually used for industrial purposes, had caused hundreds of children in the Chinese mainland to develop kidney stones, with a few cases of death.

Hong Kong reported the first confirmed case of child kidney stone on Saturday, followed by a second case on Monday.

The HKSAR government had its revised Harmful Substances in Food Regulations gazetted with immediate effect on Tuesday, limiting the level of melamine in food.

The Center for Health Protection received 651 hotline enquiries related to melamine-tainted milk by 1:00 p.m. Tuesday, with 157 of the affected persons saying that they had symptoms of renal problems including dysuria and abnormal urination.

Chief Executive Donald Tsang announced on Tuesday that a task force involving different departments will be established to tackle the long-term issues.