The world is at a crucial turning point in its battle against the swine flu virus, a top UN official said today.

World Health Organisation deputy chief Keiji Fukuda was speaking as the WHO raised its alert level to four – two steps short of a full pandemic.

The virus has now spread across the globe with new cases emerging almost by the hour today.

The US, Canada, Spain and Britain confirmed cases earlier but no deaths have been reported outside Mexico, where 152 people have died.

Swine flu outbreaks in Europe are likely to get worse in the next few days, the European Commission warned, but the public was advised not to panic.

Health Commissioner Androulla Vasiliou said there were still only three confirmed cases in the EU, one in Spain and two in the UK, but there are suspected cases in Ireland, Denmark, Germany, Italy, Sweden, Greece and the Czech Republic.

The WHO said experts did not recommend closing borders or restricting travel. Mr Fukuda said such moves had “very little effects in stopping the movement of this virus.”

Commenting on the raising of the alert level to four, he said: “What this can really be interpreted as is a significant step towards pandemic influenza. But also, it is a phase that says we are not there yet.”

He went to say that “a pandemic is not considered inevitable”.

Professor Sir Liam Donaldson, the Government’s Chief Medical Advisor, said: “The WHO has changed the alert to stage four. This means there are small clusters of outbreaks with limited person-to-person transmission.

“From some affected areas, it appears that early doses of anti-virals such as Tamiflu are helping people to recover.”

He said there was enough anti-viral drugs to treat “half the population”.

“We have been preparing for the possibility for a number of years and are among the most prepared countries in the world,” he said.

Dr Maureen Baker, the honorary secretary of the Royal College of GPs, said family doctors should reassure patients that they can expect to recover from flu within a week, even if it is swine flu.

She told the BBC Radio 4 Today programme: “GPs should be saying to people not to panic, that we are well prepared and that most people who get ill with flu will have a nasty bout of flu and get better within a week, even if it is swine flu.”

By David Burrows