The weather has gone from bad to worse in Wellington.

A major thunderstorm struck the city just after seven o'clock, causing flash flooding on roads and parks.

Newstalk ZB reporter Felix Marwick says even by windy Wellington standards the conditions are extreme.

"Lot's of lightning, lots of thunder, lot's of blocked drains, and fairly atrocious conditions all around."

Marwick says the worst flooding is in low-lying suburbs.

The floods have affected several highways.

The Newlands on- and off-ramps at State Highway One are closed.

The Johnsonville south-bound off-ramp has recently reopened.

Part of the JVL train service has been replaced by buses because of a slip near Johnsonville.

There's also flooding on State Highway Two at Horokiwi northbound.