About 25 million people, or some 20 percent of the population, are expected to become infected with swine flu, the Health, Labor and Welfare Ministry said Friday.

Some 380,000 people, or 1.5 percent of the anticipated cases, are expected to be hospitalized and 40,000, or 0.15 percent, are expected to develop serious symptoms like encephalopathy or need to be aided by respirators, according to the ministry's estimates.

Meanwhile, the National Institute of Infectious Diseases said in a report Friday that about 150,000 people probably caught some form of the new H1N1 strain of influenza in the week that ended Sunday.

The health ministry anticipates that the epidemic will peak around late September to early October.

Some regions, including urban areas where the population is concentrated and rural areas with many elderly people, may see more than 30 percent of their populations infected.

In those areas, the rate of hospitalization may hit 2.5 percent and the percentage of serious cases of infections may reach 0.5 percent.

"The figures do not take into consideration the effects of vaccinations. Actual figures will be affected largely by contact between people in each community and weather conditions," a ministry official said. "But the situation may turn worse if the virus becomes more virulent."