The number of confirmed cases of swine flu has risen to 1,200 in 20 countries, the World Health Organization said Monday, after UN Secretary General Ban Ki-moon said the health agency has no immediate plans to raise its pandemic alert to the highest level.

A security guard wears a protective mask as a precaution against swine flu as he stands in the airport in Tijuana, Mexico, on Sunday. (Guillermo Arias/Associated Press)Keiji Fukuda, the UN health agency's acting assistant director general, told reporters on Monday the WHO has concerns about the infection travelling to the southern hemisphere as that part of the world heads into the winter months, when influenza viruses usually occur.

The largest number of H1N1 flu cases reported are in North America, Fukuda said, while new cases being reported in Europe are related to travel. He said there is still no evidence of community-level spreading of the virus in Europe and Asia.

"We're not quite certain how this is going to evolve," Fukuda said during a video teleconference from Geneva. "There is always uncertainty about the evolution of a new disease as it spreads worldwide."

He added that the global tracking of the situation is the "best surveillance we've ever had."

The total number of confirmed swine flu cases in Canada rose to 140 on Monday, as Nova Scotia, Ontario, Alberta and New Brunswick reported new cases, and Prince Edward Island confirmed its first two cases.

No rise in pandemic alert level

The global pandemic alert is at Phase 5, its second-highest level. Phase 5 is called when there is human-to-human spread of a virus in at least two countries in one region, according to WHO's pandemic response guidelines.

The classification means a pandemic is imminent and countries must finalize preparations to deal with the outbreak of swine flu.

To declare a full-blown pandemic, WHO would have to be convinced the new virus is spreading in a sustained way among communities in another region besides North America.

Earlier Monday, WHO director general Margaret Chan told the UN General Assembly there was "no indication" that the outbreak is similar to a pandemic in 1918 that killed tens of millions of people around the world.

In comments published in a Spanish newspaper earlier on Monday, Chan also indicated the organization must be open to all possibilities and said raising the pandemic alert to its highest level would not mean "the end of the world."

Chan told El Pais that it's important to inform people about the levels before Phase 6 is reached.

"Level 6 does not mean, in any way, that we are facing the end of the world," Chan said in the interview published on Monday. "It is important to make this clear because [otherwise] we when we announce Level 6 it will cause an unnecessary panic."

70 Mexican travellers quarantined in China

Meanwhile on Monday, Mexico sent a chartered jet to China to retrieve citizens who have been quarantined amid fears about the spread of swine flu.

Chinese health officials have quarantined more than 70 Mexican travellers even though none is suffering from the H1N1 virus.

"In many cases we have gotten reports that they were being quarantined for the sole fact that they had a Mexican passport, whether or not they came from Mexico, whether or not they had been in Mexico, whether or not they had been in contact with someone else from Mexico," said Jorge Guajardo, Mexican ambassador to Beijing.

Officials with Mexico's Foreign Relations Department have confirmed that a chartered jetliner was being sent to China on Monday to return any citizens who wanted to leave China. A written statement said the plane would go to several Chinese cities "where Mexicans have expressed their intention to return to Mexico."

Chinese authorities have also tracked down and quarantined passengers who were on the same flight as a Mexican traveller who was diagnosed in Hong Kong with swine flu last week. None has shown symptoms of the virus, the Health Ministry said.

The hotel in downtown Hong Kong where the sick passenger stayed has quarantined its guests and staff for one week.

Mexicans not singled out: China

China's Foreign Ministry has insisted that Mexicans are not being singled out.

"The relevant measures are not targeted at Mexican citizens and are not discriminatory. This is purely a question of health inspection and quarantine," the ministry said in a statement.

It is believed that the outbreak of the swine flu virus began in Mexico, where there have been at least 727 confirmed cases and 26 deaths.

It is up to each country to determine how it attempts to control the outbreak of the disease, said Hans Troeddson, a WHO spokesman.

"It's really up to each country and should be in accordance with their own regulations and legislation on public health and protection of the population," Troeddson said.

Chinese officials have detained about 25 Canadian students at the Beijing airport and ordered them quarantined for seven days.

Beijing has banned imports of pork from Mexico, some U.S. states and Alberta, despite the WHO assuring that the virus is not spread through the consumption of pork. Direct flights between China and Mexico have also been cancelled.

Mexico to loosen shutdown

Also Monday, Mexico, which is in the last day of a five-day shutdown of non-essential services, announced most of the country's businesses would re-open on Wednesday.

Health Secretary Jose Cordova Villalobos said the outbreak in Mexico is waning, which means cafés, museums and libraries will also be reopened this week.

But he said health officials need to finish inspecting schools before students can return to class. President Felipe Calderon said university students can go back to school on Thursday and all other students will return to class next Monday, following nationwide school shutdowns that began April 27.

Despite Mexico's optimism that the worst may be over, the WHO warned against over-confidence because specimens are continuing to be tested and because the southern hemisphere is entering its flu season.

The first confirmed case of swine flu in South America was found in Colombia on the weekend.

Portuguese officials reported on Monday that they have confirmed their first case of swine flu. The patient, who is recovering, had recently returned to Portugal from Mexico, officials said.

With files from The Associated Press