The force of the rainwater caused huge cracks to open up along main roads and lifted manhole covers clean off, leading to fountains of water gushing out.
At a beach in Bournemouth - which is normally crowded with holidaymakers at this time of the year - water was flooding off the road, along the beach and into the sea.
© BNPS.CO.UKI don't like to be beside the seaside: A torrent of water swept onto the beach causing lifeguards to run for cover. If you have any pictures of the downpour, please send them to mailonlinepictures@dailymail.co.uk
© BNPS.CO.UKWater floods out of a drain as the sewage system fails to cope with the sudden downpour in Bournemouth
Meteorologists said 30mm of rain - just over an inch - fell in a few hours which is just over half of a month's rainfall.
Some areas had a months worth of rain in a morning - with over 60mm falling in Bournemouth between 6am and midday. 56mm of rain falls in Bournemouth in an average August.
An army of 100 firefighters worked to pump floodwater away after being inundated with more than 70 reports of flooding in a 30-minute spell.
A ceiling at the Bournemouth International Centre concert venue collapsed under the sheer weight of rain.
A three mile section of the A338 - the main road into the seaside town - was also closed after being swamped by 3ft of water, bringing travel chaos to thousands of motorists.
© Darren CraigA man paddles across Bournemouth gardens past the bandstand in a kayak today after a sudden downpour caused flash flooding
© Amy MatthewsA man appears to be in difficulties as he paddles across Bournemouth pleasure gardens today. This picture was provided by MailOnline reader Amy Matthews
© BNPS.CO.UKGoing nowhere: Water laps up to the doors of a police car as it lies stranded in the rainwater
© Caters News AgencyThe road cracked open in Bournemouth as thousands of gallons of water poured into the drains as two weeks rain fell in half an hour
© BNPS.CO.UKAn August morning? With a darkened sky this car was forced to put its headlights on as it edged through Bournemouth this afternoon
'There were loads of people grabbing any sort of shelter they could find, some were paddling in the water streaming down the streets.
'The central gardens were completely under water and huge cracks opened up in the main road in the town centre.
'I heard a loud crack but it was only when the water level started to drop I saw the crack was about 20ft long. It was chaos.'
© INSFlooding: A roundabout is flooded in MAIDENHEAD, Berkshire, today as more than 40mm of rain fell in the area in the space of a few hours
© BNPS.CO.UKFlash flood: Bournemouth pleasure gardens were almost completely underwater after a fortnight's worth of rain fell in just half an hour
© RexA road is flooded underneath a railway bridge in the centre of READING, Berkshire, after a huge downpour today
© Jon SavageHeavy rain also caused flooding in DUNBAR, East Lothian. Here a cyclist struggles to make his way down the road following flooding
© Jon SavageThe whole of Britain was hit by a heavy downpour. Here there is flooding in DUNBAR, East Lothian
'Flash flooding in the Bournemouth area has meant we have had to temporarily close the Nuffield Health Bournemouth Hospital to incoming patients,' a spokesman said.
'Staff are currently contacting all patients due to visit the Hospital today for both in and out-patient treatment, to inform them not to visit and to explain that all consultations and treatments have been suspended until further notice.'
© BNPS.CO.UKA bus station is flooded in the centre of Bournemouth. A whole months worth of rain had fallen by early afternoon
© BNPS.CO.UKA road is partially flooded in the seaside town after half an hour of heavy rain
© BNPS.CO.UKWashout: Firefighters were called out 70 times in an hour as tourist attractions were drenched in rainfall
© Michael HansfordMailOnline reader Michael Hansford provided this picture of flooding in the centre of Bournemouth which was hit by a fortnight's rain in half an hour
© BarcroftUnderwater golf: A crazy golf course in Bournemouth begins to reappear as floodwater drains away
© BarcroftTourists and locals who had gathered at the sea front to watch the opening day of the 4th Bournemouth International Air Festival have to take a detour to get into the town centre
'Problems were reported at the Russell-Coates Museum, House of Fraser, Primark, Beales and many other shops in the town centre.
'Many people were stranded in water on the roads where police vehicles couldn't reach them, so we sent wading teams in to help.
'One car in Wimborne was seen to float away with an elderly couple inside and members of the public helped push it back onto land.'
© BarcroftClear-up: Wessex Water use pumps to remove the floodwater from Bournemouth after the sudden downpour
© BarcroftAn industrial estate is flooded in POOLE, Dorset, after the River Bourne broke its banks
© BarcroftSummer-wear: Tourists in Bournemouth, Dorset, after the downpour today
© UnknownFlash flooding in Bournemouth Gardens today.
© BNPS.CO.UKWhere's are the flowers? Bournemouth Pleasure Gardens today
© BNPS.CO.UKNo weather for shorts: A postman bravely cycles through the heavy rain
© BNPS.CO.UKWet wet wet: Water sweeps down from Boscombe Chine Gardens to the sea after 30mm of rain fell
© Dan RedfearnFlooding in gardens in the centre of Bournemouth caused by the heavy rain.
'We've had 30mm of rain this morning. The average rainfall for August in 56mm, so it is around half that in just one morning,' he said.
'Anything over 4mm of rain in an hour is considered 'heavy' so this was well beyond that level.
'The rain was forecast, caused by a warm front over the English Channel which is heading north-eastwards, but the amount was underestimated.
© GettyFlashback: Sunseekers pack a beach in Broadstairs, Kent, two weeks ago as temperatures hit 29c
anyone else think that looks like more than an inch or two of rain?