Pharmaceutical firms in China and India say they can quickly ramp up production of antiviral drugs if swine flu threatens the world's two most populous nations or if other countries need it.
The virus could spread quickly in densely populated cities in China or India where healthcare systems are often inadequate and antibiotic resistance is common, health officials say.
But so far there have so far been no confirmed or even suspected cases of the virus in either China or India, where more than one out of every three humans live.
Since avian flu caught the world off guard in 2003, Swiss drugmaker Roche Holding AG has authorized drug companies in developing countries to manufacture an inexpensive generic form of its Tamiflu drug, called oseltamivir or Fluvir.
Hyderabad-based Hetero Drugs, the only supplier in India licensed by Roche, could ramp up production to reach monthly capacity of about 80 million doses of Fluvir within weeks, Managing Director Srinivas Reddy said.
"We have told them we are keeping 1 million doses ready for them, which we can supply in 4 to 5 days," said Reddy, referring to the Indian government.
India's government has already stockpiled one million doses, which could treat more than 142,000 people.
Hetero supplied 200 million doses of the drug in the last three years to India and other countries, Reddy said, adding nations in Latin America, Middle East and Southeast Asia had inquired recently about it.
While there is no vaccine for the swine flu that has killed up to 159 people in Mexico, the generic drugs have been shown to be effective in treatment.
In China, only two companies are licensed to produce generics and they must supply directly to the government at regulated prices and not through regular commercial channels.
"I believe we have sufficient capacity to meet the government's needs in the case of any emergency," Tu Langou, director of global business at HEC Pharm Co, told Reuters.
GlaxoSmithKline's Relenza has also been shown to be effective against swine flu, but it is more complicated to make and ingest.
India does not currently stockpile Relenza doses.
Vineet Choudhary, a senior official at India's health ministry, said the government had "millions" of face masks available for distribution, a key weapon against a virus that is spread by droplets.
The government will also shortly step up surveillance at India's international airports and ports, said Choudhary.
China has shown that it can react quickly in national emergencies, mobilizing local and national governments, along with the military to deal with last year's devastating earthquake and freak winter storms.
HEC has not yet been asked, however, to begin production of oseltamivir, perhaps because Beijing has anyway been stockpiling the drug over the past two years, said Tu.
"HEC has supplied a great quantity over the past two years to government warehouses," he said. Tu did not reveal any details on capacity or doses shipped to the government.
The World Health Organization recommended that governments stockpile antiviral drugs after the Avian Flu in 2003.
Roche came under criticism for guarding the rights to Tamiflu too closely after the Avian flu erupted, but eventually licensed rivals in developing nations to help meet soaring global demand and slow its spread.
HEC, Shanghai Pharmaceutical group and the Indian companies were providing the drug at reduced prices to ensure it gets into the hands that need it most.
"We do not make money from this program," said HEC's Tu.
Amar Lulla, joint managing director of Indian drug maker Cipla Ltd said the company had the capability to supply 1.5 million doses of oseltamivir in four to six weeks.
Cipla's cheaper version of Tamiflu costs about $1 a capsule for export markets, slightly more than Hetero's 10 doses for about $6.0.
"We have received some enquiries from Mexico, Israel, New Zealand and Latin America, but nothing has been finalized in terms of exports," Lulla said.
Cipla has not received any request from the World Health Organization to supply the drug, but the Indian government had asked whether it could supply the drug and had been told it could.
Ramesh Adige, president of Ranbaxy Laboratories, the third supplier in India, said his company was also prepared to begin supplying a generic version of the drug if needed.