In the past week doctors have reported 17 suspected cases of flu per 1,000 inhabitants, the Federal Office of Public Health said on Wednesday.
This corresponds to 144 cases per 100,000 people.
The level at which winter influenza cases are considered an epidemic is 68 cases per 100,000 residents, the Health Office said.
It said the group most affected was children aged up to four years with an estimated 234 cases per 100,000 inhabitants.
Incidences of flu are most widespread in western and central Switzerland, especially the cantons of Geneva, Neuchâtel, Vaud and Valais.
Least affected are Zurich and the northeastern cantons.
Most European countries are currently reporting a low to average incidence of flu-like infections but these are on the rise, according to the Health Office.