Flooded homes along the River Thames are being evacuated and thousands more are at risk, with water levels expected to keep rising for the next 24 hours.
Residents in one Berkshire village say the scenes are from a "horror movie". Fourteen severe flood warnings are in place in Berkshire and Surrey, while two remain in Somerset.
PM David Cameron, who is in flood-hit south-west England, said it was not the time to change personnel amid criticism of Environment Agency head Lord Smith.
Homes, shops and businesses in the Berkshire village of Datchet are underwater and hundreds more along the lower River Thames, as far as Shepperton, are under threat, the Environment Agency says.
Several Thames gauges are showing their highest levels since being installed in the 1980s and 90s.
Fire crews, who have been rescuing people from their homes in Staines-upon-Thames, say they have never known waters so deep or a flood rescue operation on this scale.