An ammonia leak from a cold storage unit at a food company in China's commercial hub of Shanghai killed 15 people on Saturday and sickened dozens, the city government said.

The leak sickened 26 people, who had been sent to hospital, with six in critical condition, the Shanghai government said in a statement.

The accident occurred shortly before midday in the northern district of Baoshan due to a leaking pipe linked to a refrigeration unit owned by a seafood company, media reports said.

More than 200 firefighters were deployed to the scene, using water to disperse the liquid ammonia and its fumes, the Xinmin Evening News said.

Photos on the newspaper's website showed fire engines at the scene with hoses on the ground and a truck used to monitor environmental pollution.

The government did not say whether the company's workers or people living in the urban area nearby were affected.

Liquid ammonia used in refrigeration can destroy lung tissue, potentially resulting in death, and cause chemical burns on the skin, according to the US Occupational Safety and Health Administration.

Shanghai environmental officials denied a "pungent smell" in the area earlier in the day was caused by the ammonia leak.

The food company involved, Shanghai Weng's Cold Storage Industrial Co., is engaged in the import and export, storage, processing and sales of aquatic products.

It has the capacity to freeze 150 tonnes of products a day, according to its website.

Shanghai is considered to be more tightly regulated than other cities in China, but this marks the second accident at a food company in the city in less than a month.

On August 20, five workers at a local food company died after inhaling poisonous fumes while cleaning a vat used for making pickled vegetables, according to the government.

China has a dismal record on industrial safety as lax enforcement of laws causes business owners to cut corners or offer bribes to evade standards.

More than 27,700 people were killed or went missing in workplace accidents in the first half of this year, state media have reported.

A total of 226,048 workplace accidents occurred in the first half, down 3.8 percent from the same period last year, the China Daily newspaper said.

A fire caused by an ammonia leak at a poultry processing plant in the northeast province of Jilin in June killed more than a hundred people.