Storm and torrential rain weather warning for Wales
Torrential rain has been forecast for Wales, prompting the Met Office to issue an amber "be prepared" warning.
Officials say flooding of homes and businesses could "happen quickly" as a band of rain sweeps in from the south west.
As well as the rain, lightning, hail and strong winds are also predicted.
A Met Office spokesman said: "There is the potential for 30-40 mm of rain to fall in an hour and perhaps as much as 60-80 mm in two to three hours."
The amber warning covers all of south and mid Wales and is in place until 06:00 on Friday.
A yellow "be aware" warning is in place across the country and is expected to last until 09:00.
Fire services reported isolated incidents of flooding.
Three or four properties in Newtown were flooded on Thursday evening following a thunderstorm that moved into Powys from Shropshire.
There were also reports of flooding in the Square, Blaenau Ffestiniog, where blocked drains may have failed to cope with heavy rain from a thunderstorm.
Asda in Cwmbran, Torfaen, had to close due to rain coming through the roof but the store is expected to reopen later.
In response to the warning, Network Rail has introduced speed restrictions across many parts of the Great Western network.
Trains are not allowed to exceed 50mph (80km/h) from 16:00 on Thursday until 06:00 on Friday.
A Great Western Railway spokesman said this would "significantly impact" its services and would result in last-minute cancellations and delays.
Ticket restrictions have been lifted so people with off-peak tickets can travel during peak times and anyone choosing not to travel on Thursday will be allowed to do so on Friday instead.