A lifeboat team rescued 20 men, women and children from a food store in flood-hit Uckfield, including trapped night workers.
The party, including staff stuck in the Somerfield supermarket and others from flats above the shop, were moved from the town centre to safety.
It was the first evacuation by RNLI volunteers who went to the scene from Shoreham, Brighton, Eastbourne and Hastings.
Those rescued were taken to two rest centres set up by Wealden Council at a local school.
Police said a further 120mm of rain was expected to fall at any time.
Officers urged drivers to stay at home and those who do have to travel to slow down.
Superintendent John Drunsfield, divisional commander for the Uckfield area, said: "There are lots of problems in villages in the area.
"People are driving far too fast and having minor accidents which we are then having to clear up.
"There is water on the roads that may appear to be just puddles to drivers but which are actually very deep. People should just slow down."
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