Washington - The United States braced for worse from the swine flu outbreak Tuesday as officials warned of potential deaths, California declared a state of emergency, and New York closed a second school.

US President Barack Obama asked Congress for an extra 1.5 billion dollars to boost preparations for a worst-case scenario. The White House said that 12 million doses of anti-viral drugs were being distributed to the states most affected.

The number of swine influenza cases in humans in the United States increased officially to 64 in five states, the US Centres for Disease Control and Prevention (CDC) said Tuesday. CDC acting director Richard Besser said that the number would likely increase Wednesday as states collect information.

"We will see deaths from this infection ... in this country," he warned.

Unlike Mexico, where 152 deaths from influenza have been reported, including 20 confirmed as swine flu, there there have been no confirmed deaths in the US. A California newspaper quoted a local medical examiner as saying there may have been one or two deaths from flu.

California reported four more infections Tuesday, bringing the state's total to 11. Governor Arnold Schwarzenegger declared a state of emergency, and health officials closed a school in the state capital, Sacramento.

"While there is no need for alarm, it is the governor's top priority to limit the swine flu's spread as quickly and effectively as possible," Schwarzenegger's office said.

The worst-affected state was New York, with New York City having 45 confirmed cases. There could be several hundred or more cases of illness, Mayor Michael Bloomberg said. Health officials shuttered a second school, Public School 177, in the Queens borough, after last week closing a nearby parochial high school, St Francis Preparatory.

A Catholic school on Manhattan's Upper West Side was being investigated for a possible outbreak, Bloomberg said.

There were six cases in Texas, two in Kansas and one in Ohio.

People who have fallen ill in the US range in age from 7-54 years, with a median age of 16 years. At least five people have so far been hospitalized - three in California and two in Texas.

Secretary of Homeland Security Janet Napolitano warned that the outbreak could wane over the summer, when hot weather is known to kill viruses, only to have a "resurgence in the fall." In the 1918 "Spanish flu" pandemic, a milder flu outbreak was seen six months before the most devastating wave.

The White House said the federal government was stockpiling anti- viral drugs and working to develop and "ramp up production" of a vaccine. White House spokesman Robert Gibbs denied that the request for more money indicated a new level of concern by the White House.

There is still no vaccine to treat this strain of swine flu in what Besser called a "pre-pandemic" period, and existing seasonal flu vaccines lack protective value against this new strain.

US pork producers and federal officials, along with their counterparts in the European Union, worried that the term "swine flu" would hurt pork sales and launched a debate about changing the name.

"Change the name of this flu! It's H1N1!" demanded Tom Vilsack, Obama's agriculture secretary. He said that close monitoring of the nation's pork industry shows no illness among hogs.

Even CDC's Besser said that the name swine flu implied "transmission from pork products, and that's not helpful to those who produce pork and those who eat pork."

Keiji Fukuda, World Health Organization (WHO) assistant director- general for health security, said that the outbreak "started with that name" and there were no plans to change.

China, Ukraine and other countries have banned pork products or live swine imports from Mexico and the United States.

"There is no danger from eating pork. If you cook pork well, any meat well, it kills any virus," WHO spokesman Gregory Hartl said.

In response to the intensifying outbreak, the World Health Organization (WHO) has raised the worldwide pandemic alert level to Phase 4, defined partly by a scientific finding that the virus is spread through sustained person-to-person contact. No one has a natural immunity to the new strain.

The CDC and State Department are urging against non-essential travel from the US to Mexico, in effect through July.

Health experts were struggling to understand the new flu strain, which has genetic elements that come from three species - pigs, birds and humans - and has never been seen before. They were still looking for the origins of the virus.

People suffering from swine flu display the same symptoms as seasonal flu.