Torrential downpours and flooding have swamped parts of London and the South East in the early hours of EU referendum day, with the fire brigade inundated with more than 300 emergency calls.
Red "immediate action" flood warnings were issued for parts of south-east London and Essex as parts of the capital were expected to see a month's rain fall in a matter of hours.
London Fire Brigade (LFB) said it received a day's worth of calls in just an hour and a half to reports of weather-related incidents including lightning striking property, flooded homes and businesses and rising waters trapping vehicles.
There were reports of flooded streets as storms swept through, threatening disruption as voters head to polling stations.
An LFB spokesman said: "Crews are being mobilised to incidents as quickly as possible but the Brigade is appealing to people to only call 999 in an emergency - where there is a risk to life or property.
"Between around 1.30am and 3am our control officers took over three hundred calls - around as many as they would receive in an average day."
In just one hour, 20.5mm of rain fell in Bexley, East London, close to half the June average, with some parts expected to see multiple showers bringing a month's rain on Thursday morning.
The Environment Agency has issued four flood warnings covering rivers in Bromley, Sidcup and Basildon, and 22 flood alerts across of the South East.
Showers are expected to ease by 10am on Thursday morning before returning with similar intensity from 2pm.
The Met Office issued an amber "be prepared" warning of rain for part of Kent, Sussex and Surrey effective until 6am on Thursday, while a yellow warning covering the South East is in place until 6am on Friday.
Forecaster Luke Miall said: "If you draw a line from The Wash to the Isle of Portland everything east of that is in the firing line.
"A band of showers is coming across the English Channel and moving north-eastwards, that will bring some heavy downpours and localised surface flooding. There's going to be a bit of hail in there too, so there's quite a lot going on.
"If you're in the South East, you definitely need your umbrella and possibly a pair of Wellington boots."
The storms threatened widespread travel disruption across the south, with Abellio Greater Anglia, South West Trains and Southern all warning of major delays on some routes.
In London parts of the underground and overground railway were suspended due flooding.