After the bird flu crisis in 1997, the bureau agreed to implement a system to monitor chickens being exported to the SAR, he said.

Farms are registered and all export chickens must be quarantined for five days before leaving Shenzhen. Mainland vets inspect all export chickens and random blood samples are taken to test for traces of the deadly flu strain.

Vets also inspect chickens at the Man Kam To border.

'These are procedures both sides agreed to. Our 40 vets work day and night at the border and on farms,' Mr Tan said. 'Now that you have problems there, you shouldn't point the finger at us. Accusations in some of the Hong Kong newspapers are totally irresponsible.'

There are 184 registered chicken farms in Shenzhen that supply Hong Kong with an average of 100,000 chickens a day, or 30 million a year.

'I can assure you all of these 30 million chickens are healthy and clean,' he said.

But Mr Tan would not be drawn on whether his remarks suggested the source of the outbreak was in Hong Kong. 'That I won't say for sure because there could be many sources.'

Mr Tan said that neither the Hong Kong Government nor the World Health Organisation had contacted his quarantine bureau over the outbreak.

SAR animal inspectors have given a clean bill of health to all local chicken farms and the Cheung Sha Wan wholesale chicken market.

Dr Howard Wong Kai-hay, senior veterinary officer of the Agriculture, Fisheries and Conservation Department, said yesterday there was no evidence the new strain of bird flu was affecting any of the 143 Hong Kong chicken farms or the wholesale market.

From November last year to April this year, 16,290 blood tests for bird flu were carried out on farms. Random blood tests are also taken seven days before chickens are despatched to retailers, and each farm was inspected at least 10 times during this period, said Dr Wong.

Inspectors are expected to address workers at an experimental farm today on how to avoid the spread of the virus, he said.