Fears were voiced last night that mainland eggs which may have been infected with the bird flu virus could have been imported to Hong Kong. The worries surfaced after a media report on the sudden deaths of up to 30,000 chickens in a key chicken farm in Dalian, Liaoning province . Food authorities in Hong Kong have promised to keep a close eye on the matter, but have no plan to impose an import ban at this stage. The farm, set up in 1984, is operated by the Dalian Hanwei Chicken Farm Company, a subsidiary of the Hanwei Group in Dalian. It produces about 150 tonnes of eggs a day, keeps 2 million hens and is a major supplier of eggs to Beijing and southern China, including Hong Kong and Macau. Zhang Yan, a manager at the group's subsidiary in Beijing, said in a TVB interview last night: 'I went to the headquarters in Dalian for a meeting and was told that 20,000 to 30,000 chickens died around May 4.' Ms Zhang said she was told the chickens had died after being injected with vaccine for bird flu. Hanwei Group last night denied it was a bird flu outbreak and said it was nothing unusual, the TVB report said. Hong Kong microbiologist Lo Wing-lok last night urged the government to ban imports of eggs from Dalian. Dr Lo suspected the vaccine used by the Hanwei farm had either been contaminated or was not up to standard. 'Injecting poor-quality vaccine could also cause bird flu,' Dr Lo said. He said a shortage of bird flu vaccine on the mainland sometimes prompted farms to use poorer quality substitutes. He warned the eggs could also be contaminated if the chickens were infected. A spokesman for the Food and Environmental Hygiene Department said last night it would follow up the matter with the mainland authorities. The spokesman could not confirm if the Dalian farm supplied eggs to Hong Kong. Imports of eggs to Hong Kong do not need special approval from the department. But the spokesman said imported food had to be inspected and cleared by the relevant mainland authorities. Supermarket chain ParknShop said last night it did not sell eggs supplied by the Hanwei Group. Rival Wellcome was unable to confirm whether the group was one of its egg suppliers, but a spokesman said: 'All our products have met the health standards of Hong Kong and the mainland.'