The number of swine flu cases in Japan soared over the weekend, raising the likelihood that the World Health Organization will soon have to raise its pandemic alert level to 6, the highest level.

On Sunday, the assistant principal of a school in Queens died after being hospitalized with swine flu. It was the sixth flu-related death in the United States and the first in New York State.

In Japan, authorities ordered more than 1,000 schools and kindergartens in and near the cities of Kobe and Osaka to shut down. There were no confirmed cases in Tokyo.

Until Friday, Japan thought it had contained the virus after finding four infected people who had visited North America and flown home. It quarantined them and 50 other passengers, began sending medical workers to meet each flight arriving from North America to take temperatures of those on board and told visitors they would need to have their temperatures recorded daily.