MEXICO, May 1 (RIA Novosti) - Mexico's health minister Jose Angel Cordova said that the number of people infected with swine flu had risen to 312 with 12 confirmed deaths.

The health minister told journalists: "The increase in the number of dead does not mean that more people have died in the past few hours, but that we have carried out more examinations."

Mexico has introduced a five-day closure of restaurants, cafes, bars, tourist attractions and public place in Mexico City and other town and cities to try and contain the spread of the disease.

The World Health Organization said that 257 people worldwide had officially been diagnosed with swine flu. The countries with confirmed infections are the U.S., where one boy died, Canada, Spain, the U.S., Germany, New Zealand, Switzerland, Israel, Austria and the Netherlands.

In the U.S., where more than 120 people, many of whom are children, have been diagnosed with the A/H1N1 virus, over 300 schools have been closed across the country as part of quarantine measures.

The WHO raised its alert level for a swine flu pandemic from 4 to 5, one step short of a full-scale pandemic on Thursday.

"Based on assessments of all available information, and following several expert consultations, I have decided to raise the current level of influenza pandemic alert from phase 4 to phase 5," WHO Director General Margaret Chan said.