At least seven popular brands of infant milk formula have exaggerated nutrient levels on their labels that could mislead parents, checks by the South China Morning Post found.
The quantities listed on the product labels overstated the content of three important ingredients by as much as three times, although all remained within World Health Organisation guidelines.
The checks were made after the Centre for Food Safety published a report showing that two Japanese formula brands were deficient in iodine, leaving babies who consumed them at risk of thyroid and brain damage.
Using the report, the Post compared the quantities of three other nutrients - vitamin K, vitamin B5 and iron, all essential for a baby's growth - with the product labels and found significant discrepancies.
The biggest was for vitamin B5 in Nestle NAN HA 1, in which the stated amount was three times the actual quantity. Vitamin K and iron were also heavily overstated by a quarter to more than a third.
Manufacturers said some variation was normal depending on the test methods.
But pharmacists said the difference should be no more than 5 per cent. William Chiu Chun-ming, president of the Society of Hospital Pharmacists, said: 'A difference larger than that is barely tolerable.
'The results displayed a serious problem in quality control in the manufacturing process and it may be necessary to recall the products.'
Food-labelling laws, introduced in 2010, exempt baby formula, but the food safety centre said it would investigate whether there were any breaches of other laws.
Health minister Dr Ko Wing-man said the government had started the legislative process to control baby milk nutritional standards.
He said: 'We will do our best to carry out legislation plans swiftly. However, we understand the process takes time and we will follow the guidelines given by the Legislative Council.'
The Customs and Excise Department said it would seek advice from the Food and Environmental Hygiene Department on the details of the study to see if there was any violation of the Trade Descriptions Ordinance. 'If so, the department will take appropriate enforcement actions as soon as practicable,' it said.
But a lawmaker said the government was at fault for leaving a loophole in the labelling law.
Democrat Fred Li Wah-ming said: 'These formulas can state whatever they like on the nutrition labels, without holding any legal responsibility.
'The government should be blamed for allowing this current loophole.'
Other brands with exaggerated content claims included Meiji infant formula, which overstated its vitamin K content by double. Cow & Gate, Gilbert, Glico Wakodo and Morinaga also overstated some or all of the three nutrients.
For iodine, nine brands out of 14 picked by the government for testing were found to be overstating or understating their levels - with discrepancies from 7.2 per cent to 45 per cent - although the actual amounts were mostly within WHO standards.
Sales of the Wakodo and Morinaga brands have been stopped after the centre's tests found their iodine content were below WHO standards.
'All these vitamin and minerals are crucial for a baby's growth', Dr Ellis Hon Kam-lun, professor for paediatrics at Chinese University, said. 'Inaccurate data may misinform parents when they are choosing milk suitable for their babies.'
Vitamin K is a protein required for blood coagulation, vitamin B5 helps metabolise proteins, carbohydrates, and fats.
Cow & Gate said the data listed on its labels was in accordance with their rigorous product tests and the discrepancy was within standards. Meiji could not be reached for comment.
The Consumer Council said it had received three complaints about the sale of baby milk formula.
The council's chief executive Connie Lau Yin-hing urged the government to press ahead with a law to control the situation.