UK Weather: Flooding in London after heavy rain
There were reports of vehicles becoming stranded as water quickly rose to block dozens of roads and affected underground lines.
The fire brigade said it had taken about 300 calls - mostly about flooded basements or roads - in the space of a few hours on Sunday.
An amber thunderstorm warning is in place for much of south-east England, with 75 to 100mm (3in to 4in) of rainfall forecast in some areas.
Resident Chris Date tweeted a photo of a bus in Bakers Arms, Walthamstow, saying the flood water was "above the kerb".
"It's impossible to walk on the pavement. To get on that bus the water came up to my shins. This is a canal, not a road," he said.
Cyclist Eddie Elliott, 28, told the Press Association agency he had passed the area near Queenstown Road station to find the road "totally shut down".
Mr Elliott said the flooding was the worst he had experienced in the city, and described seeing "buses stood broken down in the water".
