Firefighters were called to The Maltings shopping centre in St Albans after heavy rain caused the roof to collapse.
Fire crews across St Albans were inundated with flooding calls on Friday due to storm chaos.
An appliance was dispatched to TK Maxx, in The Maltings, following reports of a problem with the ceiling.
Lara Hejazi, spokesman for Hertfordshire Fire Control, said: "We were called at 2.13pm to a partial collapse at TK Maxx."
At the same time the stretched service was called to Victoria Street, where an office block was severely affected by rain water.
A fire crew from Hemel Hempstead dealt with the flood on the premises' third floor.
Also at 2.14pm the another appliance from St Albans was sent to Warwick Road following reports of a house flood.
Firefighters isolated the electrics and worked to remove the water.