GENEVA - The World Health Organisation on Wednesday called a meeting of its emergency flu pandemic panel as a senior official said there was no evidence that the spread of the swine flu virus was slowing.

"It's clear that the virus is spreading, we have no evidence of this slowing down," said Keiji Fukuda, WHO's assistant director general for health, security and the environment.

Instead, current evidence suggested that the world was edging closer to a pandemic, he assessed.

"So we take the information and assess the overall situation which suggests that as the outbreak evolves, we are moving closer to phase five," said Fukuda, referring to the WHO's six-scale pandemic alert rating which currently stands at level four.

The meeting of international health experts on Wednesday night could decide to increase the rating to five, a rating which signals that a pandemic is "imminent." At phase six, the world would be in a pandemic.

Before taking the alert level to five, "what we are trying to do right now is to make absolutely sure that we're dealing with sustained transmission in at least two or more countries," Fukuda said.

While several people have been infected by fellow students at a New York school, Fukuda said experts were looking for evidence that the virus was not just confined there but also being transmitted to the wider community level in the United States or another country outside Mexico.

Nonetheless, he added that the symptoms of the flu at the moment were "consistent with seasonal influenza," although it has been accompanied by more instances of diarrhoea.

Information collected so far has also not linked any infection directly to pigs, he added.

"We do not see any evidence that anyone is getting infected from pigs. This appears to be a virus which is moving from person to person," he said.

Fukuda would not speculate on the severity of a pandemic, should it occur, saying that "we just don't know what the future might hold."

"The important thing here is that we have time to prepare to take actions," he said.