Officials have released 12.5 million of the nation's stockpile of 50 million courses of Tamiflu, a drug that has shown itself at least initially to be effective against the flu virus. But the officials used cautious language in describing whether it could be contained.
In Mexico, more than a thousand people have been infected; WHO has sent a team of experts there to further study the outbreak.
U.S. airlines such as American Airlines, US Airways, Continental and United waive fees for flight changes to Mexico.
U.S. emergency departments step up efforts to control the virus should it surface.
"It's all hands on deck and we're doing fine," White House Press Secretary Robert Gibbs tells reporters at a special briefing at the White House with the nation's top health and Homeland Security officials.
Running total of confirmed cases of swine flu in the US: 11, including seven in California.
Two students in San Antonio have recovered who had swine flu, but their high school temporarily closes to keep the virus from spreading.
In New York City, eight students from St. Francis Preparatory School in Queens are designated as "probable" cases of swine flu, though not yet confirmed. More than 100 students are sick with flulike symptoms.
WHO holds emergency meeting, says outbreak has potential to become a pandemic.
A government order closes Mexico City private and public schools after Mexico reports its first lab confirmation of swine flu.
The virus has spread to California and Texas; eight Americans infected.
Some influenza experts worry the never-before-seen hybrid flu strain could spur a pandemic, and health officials are on high alert. Still, "at the early stages of an outbreak there's much uncertainty and probably more than everyone would like," says Richard Besser, acting director of the Centers for Disease Control and Prevention.
People warned to take precautions such as covering their mouths when coughing or sneezing and washing hands frequently.
ABC News' Dan Childs, Lauren Cox, Joseph Brownstein, Joanna Schaffhausen, Ammu Kannampilly, Michelle Schlief, Lisa Stark, Huma Khan, Theresa Cook and Kate Barrett contributed to this report.