An estimated 1.24 million people, mainly in southwestern and western Japan, caught influenza in the first week of January, up from around 1.01 million the previous week, a state-run institute said Tuesday.

The Ministry of Health, Labor and Welfare said the season's peak is expected run from late January to February and called on the public to wear masks or cover their mouths with a handkerchief so as not to spread flu through sneezing or coughing.

The figure was calculated by the National Institute of Infectious Diseases based on the number of patients reported by some 5,000 clinics across the country.