During a "very busy two hour period" on Friday, the fire service said it received more than 100 calls to over 30 flooding incidents in Southend.
Six people were rescued after their vehicles got stuck at a flooded roundabout on Woodgrange Drive.
The roof of the Pearl Dragon restaurant collapsed under the weight of the rain. No-one was hurt.
Crews were also sent to the Sea Life Centre, opposite the restaurant on the Eastern Esplanade, to pump water from the building.
Martin Richardson, owner of the Happidrome on Southend's Golden Mile, said the amusement arcade had been overcome by water.
"It came through the back, the side, it came through the wall, it came through the roof, the main drains," he said. "At least four of the arcades on the promenade suffered.
"It's going to be a long while before we're open."
Mark Baumann, owner of the Bourgee restaurant on the seafront, said he watched in vain as flood water entered the building.
"I've never seen rain like it," he said. "The water started to come into the restaurant, and then it went further, and further.
"It was all hands on deck - some of the customers helped to squeegee the water away."
The rain has resulted in traffic delays, with the A12 London-bound at Witham blocked by flood water.
BBC Travel has the latest on the disruption.
Six people were rescued from cars trapped in flood water, as heavy rain hit Essex overnight.