The World Health Organisation is expected to officially declare a swine flu pandemic after an emergency meeting in Geneva this morning.
It would be the first global pandemic for 41 years.
The virus first emerged in Mexico in April and has now spread to 74 countries with a reported 27,000 cases and 141 deaths.
The world is currently in phase five of the pandemic alert scale, and moving to six would trigger a large scale production of vaccines.
It would also raise questions about why the step was delayed for weeks as the virus continued to spread.
WHO chief Dr Margaret Chan quizzed eight countries with large swine flu outbreaks on Wednesday to see if a pandemic, or global epidemic, should be declared.
She later announced that an emergency meeting of the WHO's flu experts will be held today.
Dr Chan says she believes a pandemic is already under way but is seeking clear proof that swine flu is spreading rapidly from person to person outside the Americas.
"Once I get indisputable evidence I will make the announcement," she told reporters.
According to the WHO's own pandemic criteria, a global outbreak means a new flu virus is spreading in at least two world regions.
With thousands of cases in North America and hundreds in Japan, Australia and Europe, many experts say that threshold has already been reached.
Sky's health correspondent Thomas Moore said any move to declare a pandemic did not mean the virus itself was growing in potency.
He explained:"This is a marker if you like of geographical spread. It's not an indication that the virus is becoming more severe."
GlaxoSmithKline is already working with a key ingredient of the swine flu vaccine to see how quickly doses can be produced.
And other major pharmaceuticals like Sanofi Pasteur have also been working on a vaccine after WHO gave them a "seed stock" of the virus last month.
However, drug giants say it could take up to six months before large amounts of a swine flu vaccine are available.