Beijing: A delicacy made from the nest of cave swift, a species of bird that builds its nest from its saliva, may cause cancer, China's quality watchdog has said.

Cancer causing chemicals were recently detected in consignments of bird nests from Malaysia.

This is the latest in a string of controversies involving the expensive delicacy made from cave swifts' saliva.

Nine batches, weighing 73 kg, imported in September and October contained toxic nitrite and golden staph bacteria - both of which can cause blood poisoning and cancer, the General Administration of Quality Supervision, Inspection and Quarantine said.

The tainted birds' nests were intercepted and returned before they could enter the domestic market, the Shanghai Daily reported Saturday quoting the administration.

The birds' nests, produced by six Malaysian companies, were discovered in ports in Guangdong and Fujian provinces.

Earlier this year, birds' nests - used in Chinese cooking for hundreds of years - were at the centre of a scandal involving the rare red form, known as red cubilose, a variety comes from nests built on rock cliffs rich in iron.

The iron permeates into nests, giving them a distinctive red colour and making them much sought after, the daily said.

But Malaysian authorities said products labelled as cubilose are sometimes dyed red by unscrupulous sellers. Many contain excessive levels of nitrite.

In September, edible birds' nests on sale in Hong Kong were found to contain nitrite levels 31 times the limit in meat. These consignments also came from Malaysia.

(Agencies)