Parents are queuing up for health checks on their babies
Police in China have arrested 12 more people in a scandal over dairy products contaminated with melamine.
Three infants are known to have died, while thousands are ill, after being fed tainted baby milk.
On Thursday, officials in the north-western province of Xinjiang said a fourth person had died, but did not say whether it was a baby.
Meanwhile, Hong Kong is recalling products made by a Chinese dairy after some were found to contain melamine.
Eight out of 30 of dairy products made by the Yili Industrial Group Co, including milk, ice-cream and yoghurt, were found to be contaminated with the industrial chemical.
Thursday's arrests bring the total number of people detained to 18, said police in the north-eastern province of Hebei.
Suppliers are believed to have added melamine, a banned chemical normally used in plastics, to watered-down milk in order to make it appear higher in protein.
The additive is blamed for causing severe renal problems and kidney stones.
The chemical was first found in baby milk powder made by the Sanlu Group. In total, melamine has been found in products made by 22 Chinese companies.
Nationwide checks on milk powder are continuing, and police in Hebei have confiscated more than 200kg (440lb) of melamine.
Of the 18 people arrested, six allegedly sold melamine, while the rest are accused of selling contaminated milk.
Premier Wen Jiabao held a special cabinet meeting on Wednesday to address the crisis.
The State Council, or cabinet, admitted that regulations had failed to improve food standards.
"The Sanlu infant milk powder incident reflects chaos in the dairy products market and loopholes in supervision, and administration which has not been vigorous," it said.
Chinese parents who can afford it have been buying imported milk powder, with some in southern China crossing into Hong Kong to stock up on foreign brands.
The milk scandal has sparked widespread anger among Chinese parents, many of whom rely on cheap baby formula to feed their infants.
It has also raised questions about China's ability to police its food production industries after a series of health scares - and fatalities - in recent years.
These have ranged from the contamination of seafood to toothpaste and, last year, to pet food exported to the US.
Parents are lining up for health checks on their babies.
They are also expressing anger at why Sanlu took so long to make the problem public.
Tests have shown that 69 batches of formula from 22 companies contained the banned substance.
Two of the companies involved have exported their products to Bangladesh, Yemen, Gabon, Burundi, and Burma, although it is not clear if contaminated batches are involved.
The BBC's James Reynolds in Beijing says one mother told him that she was angry with both the milk producers and with what she called the "useless" quality inspection departments.