Severe flood warnings were in place across the Broads last night as a combination of strong north-westerly winds, low air pressure and high tides triggered a 10ft storm surge in the North Sea.
The Yare and Waveney, along with their broads, were expected to bear the brunt of flooding, with this morning's high tides sending salt water upstream.
Flood watches were also in place along the Thurne system, whose northern broads are among the most at risk from the sea, with budget cuts meaning maintenance of coastal defences is being scaled back.
The Environment Agency said there were "extreme risks to life and property" from Great Yarmouth to Lowestoft and along the coasts of Essex and Kent.
Thousands were being evacuated from their homes along the Suffolk coast, with many spending the night at leisure centres in Lowestoft and Leiston, and Beccles Town Hall.
Experts said improved sea defences, weather forecasting and communications would avert a repeat of the 1953 floods, where hundreds died in what was dubbed Britain's worst natural disaster.
But thousands of low-lying homes were feared to be at risk, as emergency services across eastern England prepared to deal with the aftermath.
Chilling scenario - see graphics and commentary on the BBC website.