Franc Contreras, Al Jazeera's correspondent in Mexico City, said: "People are feeling confusion because of different flu figures coming from the federal government on the one hand, and the city government on the other.

"And if you listen to government figures, they say the number of cases are begining to level off.

"But health officials across Mexico will tell you they're swamped and that their own teams have begun to get sick now."

In the US, Barack Obama, the president, asked congress for $1.5bn to fight the outbreak.

California's governor, Arnold Schwarzenegger, has declared an emergency to tackle the crisis in the state, where at least 13 cases have been confirmed.

WHO warning

The US Centre for Disease Control and Prevention on Tuesday raised the number of cases in the US to 64. One other case was reported in the US state of Indiana. 

In depth


 Q&A: What is swine flu?
 Video: Mexico's swine flu response
 Video: Countries race to contain swine flu
 Asia ramps up swine flu checks
 Fears over economic fallout mount
 Gallery: Global fears of flu pandemic
 Follow Al Jazeera's Mexico correspondent on Twitter

The World Health Organisation (WHO) warned that countries should prepare for a pandemic but said that it was not inevitable that the crisis would reach that stage.

"Countries should take the opportunity to prepare for a pandemic," Keiji Fukuda, acting assistant director-general of the Geneva-based WHO, said on Tuesday.

The warning came as New Zealand and Israel joined Spain, Britain, Canada, the US and Mexico as countries with confirmed cases of the flu.

Health experts say it was still not clear why deaths have only occurred in Mexico, but governments worldwide were taking few chances, rolling out measures to protect their citizens.

Cuba and Argentina suspended flights from Mexico and several other countries warned against travel there, despite the WHO saying that it was not recommending travel restrictions or border closures to fight the spread of the disease.

'Ineffective' measures

Gregory Hartl, a WHO spokesman, said in Geneva on Tuesday that "border controls don't work, screening doesn't work".

He said infected people may not show symptoms at airports or border crossings.

Swine flu: At a glance


Deaths:
26 confirmed in Mexico and 133 more suspected

Countries with confirmed cases: Mexico, the US, Canada, New Zealand, Spain, Israel and Britain

Countries with suspected cases: Australia, Brazil, France, Chile, Denmark, Switzerland, Austria, Colombia, Germany, Norway, South Korea, Guatemala

Safety measures:
 Schools closed in Mexico, surgical masks handed out, public events cancelled
 Airports screening of travellers from Mexico for flu symptoms
 Stocks of influenza medication increased in Europe, North America and the Middle East
 Cuba and Argentina suspend flights from Mexico
 Several countries including the US and EU issue travel warnings for Mexico. EU also warns against travel to the US
 Several countries restrict or ban pork imports from Mexico and/or the US, including China, Indonesia, Lebanon, Russia, Thailand, and Ukraine

Travel limitations such as those imposed during the severe acute respiratory syndrome (Sars) outbreak in 2003, which killed nearly 800 people, were therefore ineffective, Hartl said.

"Certainly if you feel that you are ill, you should not travel, in any case, to anywhere," he said.

The WHO also confirmed on Tuesday that transmission of the virus was human-to-human and not from animal or other contact.

"There is no danger form eating pork," Hartl said. "If you cook pork well, if you cook all meat well, it kills all viruses."

The WHO's emergency committee decided not to meet later on Tuesday to review the pandemic alert level, which was raised on Monday evening to level four from three, on a one-to-six scale.

"If the virus is an efficient virus, if it spreads easily from human to human, it will probably continue to spread," Hartl said.

"We are still at phase four because we do not have incontrovertible evidence this is an efficient spreader."

Trying to allay fears of a pandemic on Monday, Ban Ki-moon, the UN secretary-general, said: "We don't know yet which way it will go, but we are concerned that in Mexico most of those who died were young and healthy adults."

Most of the swine flu victims were aged between 20 and 50. A hallmark of past pandemics has been the high rate of fatalities among young adults.

Richard Fielding, a clinical psychologist in public health at the University of Hong Kong, told Al Jazeera that "concern is warranted at this stage but panic is not".

"The media have a role. One sees it [swine flu] described as a 'deadly influenza epidemic'. I think balanced reporting is important."

To put it in context, seasonal flu kills between 250,000 and 500,000 people across the world in an average year.

But the newly discovered H1N1 strain called swine flu is worrying because it spreads rapidly between humans and there is no vaccine for it yet.