Restaurant terraces did a brisk business as patrons took advantage of the warmer than average weather to soak in the sunshine.
MeteoNews reported highs climbed above 20 degrees in numerous cities north of the Alps under blue skies, including Basel, Zurich, Aarau and Schaffhausen.
This came a day after it hit 27 degrees in Lugano in the southern canton of Ticino, the second highest temperature ever recorded in that city in March.
On Monday, the mercury also rose to 26 degrees in Locarno, another city in Ticino.
The mildest weather so far this year is forecast to cool down a few degrees on Wednesday before warming up again on Thursday and Friday.
MeteoNews said while no records were broken for the month of March, it has never been so warm on March 18th in Geneva and Sion since the introduction of weather stations in the two cities.
Meteo Swiss recently announced that the 2013-14 winter was the third warmest recorded in the past 150 years, with average temperatures three degrees higher than normal.
The sunny week is forecast to come to an end on Saturday, however, when high temperatures are expected to fall by 10 degrees with grey skies and rain predicted, along with snow in the Alps.