MET Eireann has warned of possible further flooding tonight as businesses and householders face a multi-million euro clean-up bill after a freak storm sparked widespread flooding across Cork city and county.
Drains, culverts and rivers failed to cope with the equivalent of three weeks of rainfall falling in just two hours - with parts of Cork city and county cut-off by flood waters since 5am today.
Such was the scale of the flooding that one affluent Cork suburb - Douglas - resembled a lake this morning as floods swept through homes, businesses and even a shopping centre.
Worryingly, further heavy rainfall is predicted over the next week.
The worst flooding hit the southside of Cork city with homes in Greenmount, Bishopstown, the Viaduct, Douglas, Turner's Cross Ballyphehane and parts of Togher worst impacted.
Such was the scale of the flooding that an ESB sub-station in Douglas had to be shut-down leaving almost 15,000 people without power - with several pubs in Douglas village including Barry's and O'Driscolls left under almost two feet of flood waters.
Publican David Bowe who operates O'Driscoll's in Douglas admitted he was astonished at the sheer scale of the flooding.
"My cellar is completely full up to the top and there is three feet of water inside in the pub," he said.
"A friend of ours rang me at 4am and the minute I opened the cellar door the water started gushing out - and this cellar goes down about
20 feet or so."
Locals believe that a major drainage culvert - already swollen because of heavy rainfall over recent weeks - was simply unable to cope with the overnight deluge.
Flooding also hit parts of the northside including Ballyvolane, Glanmire, Killeens, Blackpool and Sallybrook.
The Meadowbrook Estate in Glanmire was worst impacted with five feet of flood water in some homes.
St Stephen's Hospital in Sarsfield Court was struck by lightning which started a fire on a portion of its roof.
Two people had to be treated for minor smoke inhalation as Cork fire brigade fought the blaze.
Floods also hit parts of north and west Cork - and left some rural roads totally impassable.
Clonakilty was left totally cut-off by flood waters - with the emergency services co-ordinating essential access for the sick and elderly.
Mayor Cllr Cionnaith O'Suilleabhain described the situation in the town as "a disaster" with the main street under three feet of water.
Meanwhile, Belfast was also hit by the flooding with most main routes in the south and east of the city left impassable after heavy rain caused severe flooding, police said.
Cars were submerged during a massive downpour yesterday evening.
Around 1,000 homes lost electricity temporarily and residents battled frantically using boards, brushes and whatever else came to hand to try and keep back the rising waters.
The Met Office has issued a further amber weather warning valid from 04.00 to 21.00 today, according to the Executive, and the Roads Service has brought in extra staff.
An Executive spokeswoman said last night: "There are expected to be further slow moving torrential downpours tomorrow afternoon and further flooding can be expected."
Even a police vehicle in West Belfast was submerged and officers had to be rescued from the rooftop.
A PSNI spokeswoman said: "Most of the main arterial routes in east and south Belfast are impassable due to flooding, abandoned cars and debris."
A Northern Ireland Water spokeswoman said its call centre has received 2,800 calls about localised flooding.
She added areas affected included Lisburn, Dunmurry, Belfast and Bangor.
The spokeswoman said: "NI Water have received reports of blocked sewers, reports of external flooding and reports of internal flooding which are being responded to by staff and contractors.
"Every effort has been made to alleviate the flooding in the affected areas as quickly as possible and assist with the clean-up operation."
In south Belfast several houses were flooded at Burren Way in Cregagh.
Local residents claimed they were not receiving official help or sandbags. However Belfast Council and other services have established an emergency incident centre.
Politicians urged NIW to spend more to improve their drainage systems.