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.

Addressing the issue of students getting value for money, he will challenge an "upward spiral" in university leaders' pay.
Universities will be asked to publicly justify how they can pay their heads more than the prime minister.
The question of university value has been under scrutiny, with fees increasing to £9,250 in England.
In a speech to university leaders on Thursday, Mr Johnson will call for universities to set out much clearer contracts for students on what they can expect.
He will promise better "consumer protection" for students.
An annual study has shown a decreasing sense of value for money among students - with concerns about getting fewer teaching hours than they expected.
Mr Johnson will highlight concerns over increases in vice-chancellors' pay - with dozens of university heads now receiving over £300,000 and some being paid more than £400,000.
"When students and taxpayers invest so heavily in our higher education system, value for money should be guaranteed.  Yet, I am still hearing students say that their course is poor quality.
"This is not good enough, especially when some vice-chancellors take home a wage that in some cases exceeds that of the prime minister."
There have been concerns about the rising costs of university in England - with tuition fees increasing to £9,250 and interest rates on loans rising to 6.1%.
The Institute for Fiscal Studies says that average debts for graduates will now be over £50,000 - and that interest charges will have reached £5,800 before students have even graduated.
Former education minister Lord Adonis says such high levels of interest are "indefensible" and predicts that they will be changed.
And the head of the Russell Group of leading universities has described such interest charges as "out of touch" and called for them to be reviewed.
But Mr Johnson is expected to defend the current system of student finance and university funding.

It happened at about 00:30 on Sunday and both men were taken to hospital for treatment.
Officers are now asking anyone who saw what happened or who has information to get in touch.
They want to talk to people who were in the club or in the immediate area on Saturday night or early Sunday morning and witnessed the disturbance.

Twenty hostages and two police officers died during a 12-hour siege when Islamic militants stormed a cafe in the capital city Dhaka on Friday.
England are scheduled to play three one-day internationals and two Tests in Bangladesh.
The ECB said that "safety and security of players was always paramount".
England will play all their fixtures in Dhaka or Chittagong during their month-long visit, which begins with an ODI on 7 October.
The ECB said it will consult with the Foreign and Commonwealth Office over security in Bangladesh, and would take "appropriate steps" if advised that "the environment is not acceptably safe".
Six people were rescued from cars trapped in flood water, as heavy rain hit Essex overnight.
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Universities Minister Jo Johnson is going to challenge universities over "excessive" pay for vice-chancellors.
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Two men were seriously hurt during a disturbance at the Woodburn Miners Club in Dalkeith.
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The England and Wales Cricket Board says it is monitoring the security situation in Bangladesh before England's tour in October.