German virologist Klaus Stoehr on Wednesday cautioned that the growing spread of bird flu across Germany could carry the potential for another pandemic.

"The H5N1 virus has all the characteristics necessary to trigger a pandemic," Stoehr, former head of the World Health Organization's influenza program, told the German newspaper Mitteldeutsche Zeitung.

Stoehr urged to step up preparedness efforts. "Pandemics have always occurred. Good pandemic planning is the best form of protection," he said, calling for the development of new vaccines, the global updating of pandemic response plans, and stronger monitoring of animal populations.

Bird flu has been spreading rapidly across Germany in recent weeks. The Friedrich Loeffler Institute (FLI), Germany's federal animal health agency, reported on Monday that about 500,000 poultry, including chickens, ducks, geese, and turkeys, have been culled nationwide.

"It is impossible to predict how the situation will develop, but the FLI is expecting a further increase in outbreaks and cases," institute head Christa Kuehn said.