The environment ministry predicted that the Seine would peak at 6.5 metres during the night – its highest level since 1951.
The Paris town hall admitted that the speed in the rise of the Seine had defied official forecasts.
Town hall officials admitted, however, that they had consistently underestimated the speed and extent of the rise of the river over the last three days.
Two Metro stations close to the river bank were closed after water started to leak though the walls.
An angry-looking river Seine has risen to its highest level for decades in Paris, forcing the closure of metro stations, museums and libraries.
The usually placid river turned into a broad, fast-flowing torrent of muddy water on Friday, but was forecast to peak just short of the level which would flood streets and the underground railway system.
A 6.5 metre flood level is just below the point when water might start to cascade into streets and the Metro system.
In 1910, when large parts of the French capital were flooded for six weeks, the river Seine reached a height of 8.6 metres.
The Louvre and Orsay art museums, the Grand Palais exhibition hall and two sites of the national library were closed protectively.
Severe flooding in the western suburbs of the French capital is feared on Saturday after a several days of torrential rain in northern and central France.