The fire broke out at 5.30am in a building storing antiques and liquidated goods, according to Thurgau cantonal police.
“A building has collapsed. The flames have now spread to two others,” said spokesman Matthias Graf.
Over 100 firefighters were fighting the blaze with the help of two army helicopters.
One Super-Puma employed to collect water from nearby Bodensee (Lake Constance) dispatched 4,000 litres per journey to the site of the fire.