MEXICO CITY - Millions of children, many wearing surgical masks, returned to scrubbed and disinfected classrooms Monday after a nationwide shutdown to curb the spread of H1N1 flu in Mexico. As the worldwide toll of deaths linked to the illness rose to 61, pressure increased for massive production of generic versions of expensive antiviral drugs.

Mainland China got its first confirmed H1N1 flu case -- a Chinese man who had been studying at the University of Missouri in the United States -- prompting a scramble to find and quarantine more than 200 fellow passengers on his flight to China.

Some Mexican parents were worried about sending their children back so soon.

"Imagine with this disease. What if she gets it?" said Filomena Pena Carriles, lining up outside the Ignacio L. Vallarta elementary school in Mexico City with her 8-year-old daughter Esmeralda, who wore a mask as she waited for teachers to begin checking each of the 135 students for flu symptoms.

Mexico's last confirmed H1N1 flu death occured a week ago on May 4, although several more recent deaths are being analyzed, and Mexico has confirmed no new infections since Thursday. Tests on backlogged samples from earlier deaths caused Mexico's toll to rise by eight on Monday.

"We could now be in a declining phase, toward the extinction of the epidemic, but this does not suggest a total relaxation of safety measures," Health Secretary Jose Angel Cordova said.

The H1N1 flu epidemic is continuing to spread around the globe, with international health authorities reporting more than 4,700 confirmed cases in 30 nations. There are 61 deaths tied to the virus -- 56 in Mexico, three in the U.S., one in Canada and one in Costa Rica.

Antivirals such as Tamiflu are believed to be effective against H1N1 flu if administered early, and cheap generics can easily be made in countries like India. Many rich nations sit on stockpiles of expensive Tamiflu bought from Swiss drugmaker, Roche. But poor countries generally have only enough Tamiflu to treat a tiny fraction of their populations.

Some experts called Monday for massive production of generic Tamiflu, which is patent-protected and sells for up to $100 a course.World Trade Organization rules allow poor countries to override such rights in a health crisis, but generic drug makers are waiting for the World Health Organization to order their production.

Instead, the WHO says it will secure supplies through donations or discount purchases for developing countries. Critics say that reflects a reluctant to anger leading drug companies, which have long fought to keep generics out of the market in all circumstances.

WHO has a stockpile of about 5 million Tamiflu treatment courses donated by Roche, and earlier this week, the agency began sending 2.4 million treatments to 72 poor countries. But such numbers pale in comparison to hundreds of millions of people in the developing world who would be vulnerable in a flu pandemic.

Indian pharmaceuticals giant Cipla announced Monday that it could quickly produce millions of treatments at about $12 per course as soon as the WHO places orders.

"We could make a lot more, but there needs to be firm commitment from countries and international agencies like WHO," said Yusuf Hamied, the company's chairman. "The ball is in their court."

The United States now has the most confirmed cases -- 2,532 in 44 states -- according to the U.S. Centers for Disease Control and Prevention. Mexico has confirmed 2,059 cases, including two U.S. citizens and a Scot, Cordova said.

Mexican high schools and universities restarted last Thursday. But at least seven of Mexico's 31 states put off reopening schools for younger children due to a rise in suspected flu cases in some regions.

Crews worked through the weekend to cleanse school buildings and stock them with sanitary supplies as 25 million children prepared to resume their studies. Schools were closed in the Mexico City region on April 24, then nationwide three days later.

The federal Education Department said Sunday that 88.9 per cent of the nation's estimated 250,000 schools had been cleaned and disinfected.

Secretary of Public Education Alonso Lujambio urged parents not to send their children back to school if they were sick and told teachers to be on guard. Gym classes and all ceremonies remain suspended as an added precaution, and any students with symptoms were to be stopped at the door and sent home by teams.

"School life will return to normal as long as the safeguards we have put in place are effective. Help us in this," Lujambio said.

The reopening of kindergartens and primary schools is the latest step in Mexico's efforts to restore a sense of normality after the flu scare. Businesses, restaurants and bars gradually resumed operations over the past week, and except for public servants and restaurant workers, it is less and less common to see people wearing surgical masks.

The blow to tourism and production has been severe, however. Mexico's Foreign Minister Patricia Espinosa told the Spanish daily ABC that the crisis could cost Mexico 1 per cent of gross domestic product this year.

The impact goes well beyond Mexico's borders: 30 Mexican companies have dropped out of a Shanghai trade fair May 19-21 after China withdrew Mexico's "guest of honour" status.

Mexican officials were already angry over China's quarantining of dozens of Mexican travelers, airline flight cancellations and a ban on its pork products -- part of a wider series of snubs by many nations that has left Mexico feeling unfairly singled out.

China has defended such steps as necessary to keep H1N1 flu from spreading in the world's most populous nation.

Mexico said Sunday that 13 Mexicans remained in quarantine in China and one in Singapore. Last week Mexico chartered a flight to bring home dozens of its citizens from China. It was unclear if the 14 mentioned Sunday had been placed under restrictions in China since the first group was brought home.