Beijing ? The stock price of a company at the center of China’s tainted milk product scandal plunged today as more countries expanded bans on Chinese milk products to include candies and other goods.

The tainting has sickened nearly 53,000 Chinese infants who drank contaminated baby formula and has already cost the head of the country’s food safety watchdog his job. Four deaths have been blamed on the contaminated milk powder.

One of China’s biggest milk producers, China Mengniu Dairy Co., saw its stock price plummet almost 60 percent in Hong Kong trading today after its products were found to be tainted with the industrial chemical melamine.

“The board wishes to sincerely apologize for the incident and any inconvenience caused to the public,” the company said in a statement to the Hong Kong stock exchange.

The resignation Monday of Li Changjiang, who headed the General Administration of Quality Supervision, Inspection and Quarantine since 2001, comes a year after he and the government promised to overhaul the system in response to a series of product safety scares.