MEXICO CITY: The swine flu epidemic crossed new borders Tuesday with the first cases confirmed in the Middle East and the Asia-Pacific region, as the number of deaths in Mexico blamed on the virus surpassed 150.

With the swine flu having already spread to at least six other countries besides Mexico, authorities around the globe are like firefighters battling a blaze without knowing how far it extends.

"At this time, containment is not a feasible option," said Keiji Fukuda, assistant director-general of the World Health Organization, which raised its alert level on Monday.

New Zealand reported Tuesday that 11 people who recently returned from Mexico contracted the virus. Tests conducted at a World Health Organization laboratory in Australia had confirmed three cases of swine flu among 11 members of the group who were showing symptoms, New Zealand Health Minister Tony Ryall said.

Officials decided that was evidence enough to assume the whole group was infected, he said.

Those infected had suffered only "mild illness" and were expected to recover, Public Health Director Mark Jacobs said. There are 43 more suspected cases in the country, officials said.

The Israeli Health Ministry on Tuesday confirmed the region's first case of swine flu in the city of Netanya. The 26-year-old patient recently returned from Mexico and had contracted the same strain, Health Ministry spokeswoman Einav Shimron.

Dr. Avinoam Skolnik, Laniado Hospital's medical director, said the patient has fully recovered and is in "excellent condition" but will remain hospitalised until the Health Ministry approves his release.

Another suspected case has been tested at another Israeli hospital but results are not in, the ministry said.

Meanwhile, a second case was confirmed Tuesday in Spain, Health Minister Trinidad Jimenez said, a day after the country reported its first case. The 23-year-old student, one of 26 patients under observation, was not in serious condition, Jimenez said.

With the virus spreading, the U.S. prepared for the worst even as President Barack Obama tried to reassure Americans.

At the White House, a swine flu update was added to Obama's daily intelligence briefing. Obama said the outbreak is "not a cause for alarm," even as the U.S. stepped up checks of people entering the country and warned U.S. citizens to avoid nonessential travel to Mexico.

"We are proceeding as if we are preparatory to a full pandemic," said Homeland Security Secretary Janet Napolitano.

The European Union health commissioner suggested that Europeans avoid nonessential travel both to Mexico and parts of the United States. Russia, Hong Kong and Taiwan said they would quarantine visitors showing symptoms of the virus.

Mexico, where the number of deaths believed caused by swine flu rose by 50 percent on Monday to 152, is suspected to be ground zero of the outbreak. But Mexican Health Secretary Jose Angel Cordova late Monday said no one knows where the outbreak began, and implied it may have started in the U.S.

"I think it is very risky to say, or want to say, what the point of origin or dissemination of it is, given that there had already been cases reported in southern California and Texas," Cordova told a press conference.

It's still not clear when the first case occurred, making it impossible thus far to determine where the breakout started.

Dr. Nancy Cox of the Atlanta-based Centers for Disease Control and Prevention has said she believes the earliest onset of swine flu in the United States happened on March 28. Cordova said a sample taken from a 4-year-old boy in Mexico's Veracruz state in early April tested positive for swine flu. However, it is not known when the boy, who later recovered, became infected.

The World Health Organization raised the alert level to Phase 4, meaning there is sustained human-to-human transmission of the virus causing outbreaks in at least one country. Monday was the first time it has ever been raised above Phase 3.

Putting an alert at Phases 4 or 5 signals that the virus is becoming increasingly adept at spreading among humans. Phase 6 is for a full-blown pandemic, characterised by outbreaks in at least two regions of the world.

Fifty cases — none fatal and most of them mild — were confirmed in the United States. Including the New Zealand, Israeli and new Spanish reports, there were 92 confirmed cases worldwide on Tuesday. That included six in Canada, one in Spain and two in Scotland.

Symptoms include a fever of more than 100, coughing, joint aches, severe headache and, in some cases, vomiting and diarrhea.

Amid the alarm, there was a spot of good news. The number of new cases reported by Mexico's largest government hospitals has been declining the past three days, Cordova said, from 141 on Saturday to 119 on Sunday and 110 Monday.

In a bid to prevent mass contagion, Mexico canceled school nationwide until May 6, and the Mexico City government is considering a complete shutdown, including all public transportation. The Cinco de Mayo parade celebrating Mexico's defeat of a French army on May 5, 1862 and Mexico City's traditional May 1 parade were canceled. More than 100 museums nationwide were closed.

At Mexico City's international airport, families grimly waited for flights out of the capital or country, determined to keep their masks on until they touched ground somewhere else.

Three games involving Mexico City soccer clubs were played with no spectators over the weekend. Decio de Maria, secretary general of the Mexican soccer federation, said plans for future matches would be announced on Wednesday.

"The idea is to look for the fewest number of games that have to be played behind closed doors," he said. "If it's necessary, we'll play all the matches behind closed doors. We don't foresee canceling any games."

Many residents of Mexico City wore blue surgical masks, though the CDC said most masks offer little protection. Many victims have been in their 30s and 40s — not the very old or young who typically succumb to the flu. So far, no deaths from the new virus have been reported outside Mexico.

It could take four to six months before the first batch of vaccines are available, WHO officials said. Some antiflu drugs do work once someone is sick.

Napolitano, the U.S. Homeland Security chief, said Washington is dispatching people and equipment to affected areas and stepping up information-sharing at all levels of government and with other nations.

Richard Besser, the CDC's acting director, said his agency is aggressively looking for evidence of the disease spreading and probing for ways to control and prevent it.

Flu deaths are nothing new in the United States. The CDC estimates that about 36,000 people died of flu-related causes each year, on average, during the 1990s in the United States. But the new flu strain is a combination of pig, bird and human viruses that humans may have no natural immunity to.

Besser said that so far the virus in the United States seems less severe than in Mexico. Only one person has been hospitalised in the U.S.

"I wouldn't be overly reassured by that," Besser told reporters at CDC headquarters in Atlanta, sounding a cautionary note.

The best way to keep the disease from spreading, Besser said, is by taking everyday precautions such as frequent handwashing, covering up coughs and sneezes, and staying away from work or school if not feeling well.

WHO spokesman Peter Cordingley singled out air travel as an easy way the virus could spread, noting that the WHO estimates that up to 500,000 people are on planes at any time.

Governments in Asia — with memories of previous flu outbreaks — were especially cautious. Singapore, Thailand, Japan, Indonesia and the Philippines dusted off thermal scanners used in the 2003 SARS crisis and were checking for signs of fever among passengers from North America. South Korea, India and Indonesia also announced screening.

Teams of doctors, nurses and government officials boarded flights arriving in Japan from Mexico, the U.S. and Canada to check passengers for signs of the flu, Japanese Health Ministry official Akimori Mizuguchi said.

World stock markets fell Tuesday as investors worried that any swine flu pandemic could derail a global economic recovery.