Authorities in China have launched an investigation into reports of formaldehyde being used to preserve the freshness of cabbages for human consumption.

Officials in the north-eastern Hebei province confirmed that they had verified footage showing individuals dipping cabbages in a solution before loading them onto trucks for transportation.

An environmental blogger first released the footage last week. Using formaldehyde, a colourless chemical used for preserving biological specimens that is known to cause cancer, for keeping food fresh is strictly prohibited in China.

China is the world's largest producer of cabbages, most of which are exported to neighbouring countries in Asia.

Police have taken legal action against the individuals involved, according to state media.

Officials are now moving swiftly to prevent panic and restore confidence by carrying out spot checks on markets across the country.

Chinese state media says investigators will also establish how widespread the practice is and take measures to trace affected vegetables.

Local authorities in Kangbao county said in a statement issued on Saturday: "Any illegal or non-compliant practices discovered will be dealt with strictly in accordance with the law to ensure the safety of the vegetable supply."

Xinfadi market in Beijing, one of the major sources of fresh produce in the capital, issued a statement saying that it had investigated the source of its cabbages, adding that none of the affected vegetables had entered its market.

The incident has generated widespread media attention in China.

An editorial in the People's Daily wrote: "The wholesalers focused solely on their immediate economic interests while completely disregarding the lives and health of consumers. [They] crossed a legal red line and breached the moral bottom line."

China produces well over 30 million tonnes of cabbages each year, nearly half of the world's annual total. Vietnam, South Korea and Russia are among the largest export destinations for the vegetable.

Exposure to relatively high quantities of formaldehyde in some workplaces has been linked to some types of cancer in humans, but the effect of exposure to small amounts is less clear, according to the American Cancer Society.