(Adds some poultry and pig import bans, paragraphs 9-10)

BEIJING, July 25 (Reuters) - China will step up inspections on the use of antibiotics in fish farms, including chemicals that can cause cancer, after contaminants caused trading partners to block its seafood exports.

"We are focusing on getting a hold on antibiotic use, especially overuse of antibiotics on fish and crustaceans, including nitrofurans and malachite green," Zhang Yuxiang, director of the market and economic information department of the Ministry of Agriculture, told a news conference on Wednesday.

The ministry said last month that malachite green, a cancer-causing chemical used by fish farmers to kill parasites, had been found in some food samples, as well as nitrofurans, an antibiotic also linked to cancer.

China is the largest producer of farmed fish, handling 50 percent of the total value of global aquacultured seafood exports around the world. Its top export market for seafood is Japan, and it is also the third-largest exporter of seafood to the United States.

Last month, the U.S. Food and Drug Administration said a sampling of imported Chinese seafood from October 2006 through May 2007 found more than 15 percent of shipments were contaminated with antimicrobial agents that are not approved for use in farm-raised seafood in the United States.

In 2005, exports of Chinese-farmed eels to Hong Kong were found to contain malachite green.

China is under mounting pressure from abroad over food and product safety scandals, particularly from tainted pet food sent to the United States and toothpaste made using an industrial solvent.

But Beijing has insisted food safety is a global problem, and not just limited to China.

The government has banned poulty imports from Germany, the Czech Republic and the U.S. state of Virginia as well as pig products from Georgia in central Asia due to local outbreaks of animal disease like bird flu, Xinhua news agency said.

"The ban is aimed at preventing these animal diseases from infecting China, so as to protect China's animal husbandry industry and ensure public health of the Chinese," it said.

China's State Council, or Cabinet, passed a draft set of rules on Wednesday to strengthen the oversight role of local governments on food safety, which will mandate tougher fines for firms found breaking the law.

The meeting, chaired by Premier Wen Jiabao, also promised greater international cooperation, better safety checks and greater openness with quality problems, the government said in a statement on its Web site (www.gov.cn).

"Product quality and food safety have a bearing on people's health and their vital interests, trust in companies and (our) international reputation, and it must be paid the utmost attention," it added. (Additional reporting by Ben Blanchard)

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