BEIJING — The World Health Organization's flu chief urged drug makers on Saturday to donate swine flu vaccines to the world's poorest countries, which are more vulnerable in the fight against the pandemic.

Dr. Keiji Fukuda said the agency is working hard to lobby the world's rich nations and flu vaccine makers for donations.

"It is clear that the poorest countries in general are just the most vulnerable to any number of diseases, and so it is a big concern," Fukuda said on the sidelines of a symposium of health officials and experts in Beijing. "We're continually hoping that more of the companies will step up and agree to donate more of the vaccine."

WHO says the swine flu virus -- also known as H1N1 -- has killed almost 1,800 people worldwide as of Aug. 13.

For the moment, swine flu is generally mild and most people recover without needing treatment. But it could have a more devastating impact in countries where populations are also fighting AIDS, malaria, tuberculosis and other diseases.

Many rich countries like Britain, Canada and France have orders for flu vaccines to cover their entire populations. But most developing countries have no such plans.

Health officials and drug makers are considering how to speed up vaccine production before the northern hemisphere enters its flu season in coming months. Estimates for when a vaccine will be available range from September to December.

Fukuda said WHO chief Margaret Chan has met with drug makers to appeal directly, but so far only two companies, GlaxoSmithKline PLC of Britain and Sanofi-Aventis of France, have pledged to donate 150 million doses to developing countries.

Novartis AG of Switzerland has said it is looking at selling vaccines to those countries at discounted prices.

Fukuda said WHO is also exploring other options such as negotiating for the vaccines to be sold at lower prices to poorer countries and helping them set up their own production facilities.

WHO Western Pacific director Shin Young-soo said Friday he hoped China, where 10 drug makers are conducting clinical trials of flu vaccines expected to be completed by mid-September, could play a part in helping poorer countries.

Once cold weather returns to the northern hemisphere, many countries could see swine flu cases double every three to four days for several months until peak transmission is reached, Shin said.