Roads remain closed while clean-up work continues following flooding which hit parts of Gwynedd and Anglesey.
People had to be rescued from flooded vehicles in Bethesda, firefighters pumped out water from homes in Bethel and landslips blocked roads.
Llangefni town centre was flooded by 3ft (90cm) of water, with traders calling the incident "shocking".
More than 250 flood-related calls were received by North Wales Fire and Rescue Service overnight.
It said other areas affected were Menai Bridge, Rhosneigr, Bangor, Caernarfon and Pwllheli.
Llangefni toy shop trader John Hughes said the flooding was the worst he had seen in 70 years.
"I've never seen anything like it," he said.
Neil Bevan, who runs a caravan and camping supplies business, said his premises were affected by several inches of water.
"We've just got to get on with it and start mopping up and counting the costs," he said.
Virgin Trains West Coast said it had suspended services between Bangor and Holyhead due to flooding.
It warned travellers that, while replacement buses were available, services may not be able to reach all destinations due to the road conditions.
On Wednesday evening, parts of Pembrokeshire were also hit by flood water.
And in Llanfairfechan, Conwy county, residents put out sandbags to try to protect property from rising water levels
In Gwynedd, Bethel councillor Sion Jones told BBC Radio Wales' Good Morning Wales programme: "I've never before seen it like that".
"I've been here for five years and it happens every year around the same time and the same spots, unfortunately, get hit quite badly. But last night was a severe one.
"Areas were hit much worse than they have ever been hit before and new areas as well."
BBC Wales weather forecaster Behnaz Akhgar said Capel Curig in Snowdonia received 89mm of rain in 24 hours compared with 1mm at Mumbles on Swansea Bay.
Several roads remained closed on Thursday, according to Traffic Wales:
- A545 Beaumaris Road, Glyngareth, due to landslip
- A4086 at Nant Peris
- A4080 High Street, Brynsiencyn
- A4085 between Waunfawr and Rhyd Ddu
- A5025 Southbound, Pentraeth
- A4087 Bangor between Felinheli Roundabout and Cytir Lane
Beaumaris Castle moat burst its banks and flooded parts of the street and the main road into Beaumaris was also blocked last night by a landslide near Menai Bridge.
A landslide also blocked the main road through the village of Felinheli between Bangor and Caernarfon.
Residents cleared a lot of the debris to help make the road passable.
Bangor's Caernarfon Road was described by police as "doubling as a water sports arena" at one point.
Anglesey council advised staff based at its Llangefni offices to work from home if possible due to problems such as a flooded car park.
Council chief executive Dr Gwynne Jones told BBC Radio Cymru's Post Cyntaf programme the amount of rain took everyone by surprise, especially in Llangefni.
There are still flood alerts across a wider area of north Wales, Powys and Brecon Beacons.