WASHINGTON -- Congress plans to hold emergency hearings this week on swine flu.

Sen. Tom Harkin, D-Iowa, the chairman of an appropriations subcommittee dealing with health issues, called for a hearing Tuesday afternoon to explore the public health response to the outbreak.

Homeland Security Secretary Janet Napolitano is to testify before a Senate panel on Wednesday. Across the Capitol a day later, other health experts are scheduled to tell a House subcommittee about the risk of the flu spreading.

The swiftly organized hearings were inspired by the outbreak of 40 cases of swine flu in the U.S, half of those in New York City. So far, no one in the U.S. is known to have died from the illness.

The virus began in Mexico and has spread to the United States and beyond. Napolitano said Monday that travel warnings to Mexico will remain in place as long as necessary.

Napolitano said she has been in touch with Mexican officials and border state leaders to coordinate responses to the outbreak. Health officials urged Americans to take such precautions as frequent hand washing and remaining home from work or school if ill.

New Zealand reported suspected swine flu cases Monday in a second group of teenage students returning from Mexico. Asian nations with potent memories of SARS and bird flu outbreaks screened travelers for fever with thermal scanners.