Heavy downpours across England are causing major disruption for road and rail users.
Network Rail said some areas had seen two months' worth of rainfall in one day with drains overwhelmed.
Rail operator Southern has advised people to avoid travelling, delay journeys or use alternative routes.
A total of 31 flood alerts are in place across the country, with some areas set to see up to 60mm of rain, particularly over the first half of the day.
Southern tweeted that "train services running across the whole network will be cancelled or delayed".
A Network Rail spokesman said engineers were "out in force" pumping water away from areas.
"Across the south east, we suffered over a month's worth of rainfall in just one day and in some areas the downpours equated to two months' rain," he said.
"We'll continue working to keep passengers moving and then we'll review the drainage systems which have suffered problems to see if we can do any more to avoid similar incidents in the future."
In Horncastle, Lincolnshire, the River Waring was transformed into a raging torrent after hours of heavy rainfall.
Police in the town warned motorists and pedestrians "great care" was needed "due to the large amounts of surface flood water and rising drains and rivers".
Leicestershire Police said it had received a "high level" of calls about blocked roads, while a driver narrowly escaped injury when a tree fell on his car in Thurnby.
A woman in her 80s and her dog were rescued from a flooded property in West Kingsdown, near Sevenoaks in the early hours.
Kent Fire and Rescue Service said she had been trapped in her home up to waist height.
This radar map by our Flood Forecasting Centre shows how widespread and heavy the #rain has been. In Kent 104mm fell yesterday – easily more than a month’s worth of rain! As it continues you should check your flood risk: https://t.co/7eO4MuSq7i #floodaware #prepareactsurvive pic.twitter.com/0BY0GT0npx— Environment Agency (@EnvAgency) June 11, 2019
The Environment Agency said some areas of Kent recorded about 100mm of rain in the 24 hours up to 07:00 BST.
The average rainfall for the entire month of June in the UK is 73.4mm, it added.
The M25 was closed in both directions for almost eight hours earlier after two sinkholes were discovered following a crash at about 23:30 BST.
In Devon, a thatched house caught fire when it was struck by lightning overnight. No-one was injured in the blaze.
Exmoor is likely to see up to 40mm of rain on Tuesday but could have up to 60mm.
'A grim scene'
Rain has also hit the Cricket World Cup for the second day in a row as Bangladesh's game against Sri Lanka in Bristol has been called off.
BBC Test Match Special's Simon Mann said: "It's a grim scene."
The match - due to start at 10:30 - was called off shortly before 14:00.
Pilgrim Hospital in Boston, Lincolnshire, has also been hit by flooding but health bosses said patient services were "unaffected".
Fire crews have been in attendance since 03:00 pumping water out of the hospital's boiler room.
Met Office meteorologist Alex Burkill said the UK was in for "some treacherous weather".
Weather warnings are expected to remain in place for much of the day, with forecasters predicting parts of the UK could be inundated during the rest of the week.
North-eastern parts of England and the Midlands are expected to bear the brunt of the downpours on Tuesday, with a yellow warning in place until midnight.
Making plans for this afternoon? Heavy #rain will continue across parts of England and Wales, but not all areas are wet, as parts of Northern Ireland and western Scotland will enjoy warm sunshine at times pic.twitter.com/TYFi1QjAJp— Met Office (@metoffice) June 11, 2019
The Environment Agency has issued 31 flood alerts and one flood warning.
The Met Office said some parts of the country could see 60 to 80mm of rain on Wednesday and Thursday, possibly up to 100mm.
⚠️ #SNUpdates - Services on the following routes will be cancelled until further notice:— Southern (@SouthernRailUK) June 11, 2019
- Sutton to London Bridge
- Victoria to Sutton (via. Norbury)
- Victoria to Epsom
ℹ️ Full details can be found below 👇https://t.co/nUnTK53BEF pic.twitter.com/kHRoepJMFS
Mr Burkill described the figures as the "worst-case scenarios".
"If you add it all up some places are likely to see over 100mm this week, which is around double the average they would get in the whole of June," he added.