As the death toll climbed to 152 in Mexico, countries around the world took steps to warn the public and contain the rapid outbreak of swine flu, which has been confirmed or suspected in many of the deaths and illnesses worldwide.

Mexico City's government, which has closed schools and universities until May 6 and banned mass gatherings, Tuesday toughened its measures by banning diners from restaurants and ordering gyms, clubs, cabarets and billiards rooms to close.

Public health authorities were bracing for much worse with the worldwide spread of the hitherto unknown flu strain, which has genetic elements from three species, pigs, birds and humans. There is no vaccine and little natural immunity against the disease.

The United States, apparently the second-hardest hit country with 64 non-fatal cases so far, was bracing for worse as officials warned of potential deaths, California declared a state of emergency and New York closed a second school. California also closed its first school, in the state capital Sacramento.

"It is very likely we will see more presentations of serious illness and some deaths," said Janet Napolitano, US Secretary of Homeland Security, in Washington. She warned the incidence may drop off during the warm summer, which kills many germs, but resurge in the fall.

A California newspaper quoted a medical examiner as saying there may have been one or two deaths from flu.

Across the Americas, Costa Rican authorities confirmed the first case of swine flu in Central Amerca. There were suspected cases across much of Latin America: in Brazil, Argentina, Colombia, Venezuela, Chile, Uruguay and Guatemala.

Brazilian authorities - who on Monday charged that Mexico had withheld information about the epidemic too long - were evaluating 20 suspected cases across eight states, the health ministry said.

Canada's health ministry counted 13 confirmed cases.

In Europe, four cases were confirmed - two in Britain and two in Spain - even as Austria was investigating five suspected cases. Spanish officials were probing about 25 other suspected cases, and potential infections were also being investigated in the Czech Republic, Denmark, France, Germany, Greece, Ireland, Italy, Poland and Sweden.

Across Asia and the Pacific, New Zealand reported 10 confirmed cases of swine flu, and Thailand and South Korea reported suspected cases. China was investigating several suspected cases.

A common thread in the isolated outbreaks outside Mexico was travel to Mexico or contact with someone who had travelled there.

That was true of a group of infected students at St Francis Preparatory School in Queens, New York City officials said. The same applied to a group of New Zealand college students returning home from a study trip, according to the World Health Organization.

Governments scurried to cut down on unnecessary travel to Mexico. Cuba suspended all flights to and from Mexico for 48 hours, putting a crimp in much of its own tourist trade that comes via Mexico, especially for illegal tourists from the US.

The US on Monday urged people to forego all unnecessary travel to Mexico. France, Spain, Italy, Australia, India and Japan became the latest countries to follow suit. Japanese quarantine officials were boarding planes from North America to check passengers before they disembarked.

Mexican officials were alerted to the emergence of the new flu strain as illnesses continued beyond the normal season's end in February, and a woman died on April 13 in the state of Oaxaca.

Samples were taken from her and others and sent to a laboratory in Canada, where the answer came back April 23: It was positive for a new, unknown virus, a variant of A/H1N1, which originated in an animal but now, according to the World Health Organization, is being transmitted from person to person.

It was still unknown Tuesday how many of the 152 dead had died of the mutation and how many had died of common type A in influenza.

WHO has raised the world alert to Phase 4, which indicated the likelihood of a pandemic, but said this does not mean that a pandemic was inevitable.

People suffering from swine flu display the same symptoms as seasonal flu. According to the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, annual flu epidemics are blamed for more than 36,000 deaths a year. Worldwide, annual epidemics cause about 250,000 to 500,000 deaths.

The crisis had lighter moments.

Taiwan villagers were turning women's bras into face masks amidst a shortage in the shops.

In Mexico, where cinemas were shut down and football teams played before empty stadiums, the producers of the Televisa programme "Hazme reir!" (Make Me Laugh) insisted the show must go on - with plastic dolls placed in the seats usually occupied by enthusiastic spectators.