The legal action comes as the Government appeared to admit the industrial chemical melamine, toxic in large doses, may be widespread within China's food supply and not confined to the dairy industry.
The state-run media yesterday published a report saying the illegal practice of mixing melamine into animal feed to boost its apparent protein levels was an "open secret" in the food industry.
The unusual admission comes after this week's disclosure that four brands of Chinese eggs sold in Hong Kong and two mainland provinces were also contaminated with melamine. Agricultural officials suggest that the chickens must have been fed melamine-laced feed.
There have been no reports so far of any illness from eating contaminated eggs.
Shanghai's Livestock Office had earlier pledged to check whether the city's seafood supplies were contaminated by melamine and are inspecting more than 100 local feed producers.
The nine new lawsuits were filed against the Sanlu Group, in the city of Shijiazhuang, where the company is headquartered.
The melamine-tainted milk scandal emerged in September when it became public that babies who had consumed Sanlu baby milk powder products developed kidney stones.
Four babies have died from kidney failure and the Government has admitted that at least 53,000 children have been admitted to hospital.
Almost 2400 babies are still in hospital being treated, the Government said on Thursday, with one in a serious condition. More than 48,000 have recovered, but earlier in the week another 90 babies were admitted to hospitals around the country.
Sanlu knew about complaints a year ago and had confirmation of the contamination in August, but a recall was not issued until early September because of pressure from the Government to suppress bad news, including food safety issues, ahead of and during the Olympic Games.