A 23-month-old toddler has died of swine flu in Texas, the first confirmed death in the United States as well as the first outside the disease epicenter in Mexico, officials said Wednesday.

"We have confirmed the first death in this country in a 23-month-old child in Texas," said Richard Besser, the acting director the Centers for Disease Control (CDC), said on CNN.

"As a parent and a pediatrician my heart goes out to the family. As I've been saying for the past few days flu is a very serious infection, and each virus is unique so it is hard to know what we're going to be seeing," Besser added.

"But given what we've seen in Mexico we have expected that we would see more severe infections and that we would see deaths."

US health authorities on Tuesday said there were 65 confirmed cases of the H1N1 flu which is believed to have killed 159 people in Mexico.

Most of the US cases have been relatively mild, with only a handful of sufferers requiring hospitalization.

If the virus spreads broadly, the WHO has said it could heighten its pandemic flu alert to level five, which is characterized by human-to-human spread of the virus into at least two countries in a single region.

So far, the CDC has confirmed only one case of human-to-human transmission in the United States beyond people who had recently traveled to neighboring Mexico, where the outbreak has its epicenter.

The US infections were spread across six states as of early Wednesday, with most cases centered around a private school in New York City, affecting students who had recently visited Mexico.

One case confirmed on Tuesday in the midwest state of Indiana was a person who had not recently visited Mexico and so did not have direct exposure to the virus.

"It is very likely that we see more serious presentations of illness and some deaths as we go through this flu cycle," Homeland Security Secretary Janet Napolitano told reporters on Tuesday.

A state of emergency

California, which on Tuesday declared a state emergency due to the flu outbreak, ruled out swine flu as the cause of one recent death in the Los Angeles area. But the death of another man continued to be investigated after initial tests proved inconclusive.

"Because we are at the beginning of the summer, this particular outbreak may die naturally and then we could see a resurgence in the fall. This is going to be a marathon," Napolitano cautioned.

US health authorities stress that roughly 35 000 people die annually in a regular US influenza season.

But after declaring a public health emergency at the weekend, which opened up federal stockpiles of drugs and medical supplies to states, President Barack Obama did press Congress to release 1.5 billion dollars in emergency funding.

In a letter to Congress, Obama said the request was made "out of an abundance of caution" so as to "enhance our nation's capability to respond to the potential spread of this outbreak."

With US meat exports encountering new foreign bans from Russia to China, Agriculture Secretary Tom Vilsack angrily countered that there was no risk of transmission from eating pork.

Not a food-borne crisis

"It's important to get this right. This is not a food-borne crisis," he told reporters, in a message echoed by the CDC.

"We're concerned about safety but also about the impact on the economy," Vilsack said.

Already depressed by the worst US recession in decades, Wall Street stocks wobbled lower Tuesday. Airline stocks have been particularly hard hit on fears for international travel heading into the peak summer season.

The CDC is reviewing whether to change the name from "swine flu" to deal with public misconceptions, Besser said, stressing that human-to-human infection was the real risk rather than eating pork.

Apart from Indiana and California, the states of New York, Texas, Kansas and Ohio have all confirmed human swine flu cases.

One person died in the United States in s 1976 swine flu outbreak.