Two Asian groups are claiming to have produced a generic form of Tamiflu, the Roche-made medicine that may protect against bird flu.
The move could open up the bottleneck of Tamiflu supplies, which has left many countries desperately short of the anti-viral drug. Scores of people have died from birdflu in Asia, where poultry is being slaughtered to try to control the disease. It has now entered the eastern reaches of Europe.
Roche has said it will license Tamiflu to interested firms but the company claimed it was difficult to make and it would take time for rivals to develop the expertise.
However, Cipla, an Indian drugs maker, and Taiwan's National Health Research Institute, have said they had made batches of Tamiflu.
Roche has now admitted the difficulties may have been overstated.
Meanwhile, all poultry in a northeastern part of China hit by the country's latest bird flu outbreak are to be culled, the state news agency Xinhua said.
On Friday, China reported its fourth outbreak of the deadly H5N1 strain of bird flu in a month after nearly 9000 chickens died in Liaoning. About 370,000 birds were expected to be culled as police sealed the area to prevent infection.
The disease has killed more than 60 people in Asia and infected at least 123 since late 2003. In almost every case, the virus appears to have been transmitted to humans through contact with birds.
