MEXICO CITY - Mexico could lose up to $4 billion in tourism income after foreign visitors canceled trips to popular beach resorts and colonial towns due to the flu scare, Tourism Minister Rodolfo Elizondo said on Monday.

Mexico was the epicenter of a swine flu outbreak that has caused 60 confirmed deaths, according to the World Health Organization, and has spread to several dozen countries, sparking fears of a pandemic.

Tourism is one of Mexico's main dollar generators, along with oil exports and remittances sent from Mexicans living abroad.

In 2008, some 23 million visitors from abroad spent $13 billion in Mexico.

The international market, assuming the virus holds steady and the United States lifts the travel warning, could (recover) by December, Elizondo told reporters.

The U.S. government has recommended that its citizens postpone nonessential travel to Mexico.

Cruise companies, such as Carnival, have canceled stops at several Mexican ports due to the flu alert and a handful of Latin American countries temporarily suspended flights to and from Mexico.

The government closed schools in late April to prevent further spread of the infection, blamed on a new strain of H1N1 flu.

On Monday, millions of Mexican children wearing surgical masks and clutching hand sanitizer went back to classes after the two-week shutdown.