Blue lightning, marble-sized hail and patches of heavy rain have affected Wellington tonight, as a storm slowly makes its way over the city.

MetService severe weather forecaster Paul Mallinson says the intensity increased after about 8pm, dumping hail across the eastern suburbs, some of it possibly up to 20 millimetres in diameter.

A severe thunderstorm warning was issued, and in the four hours to 8.30pm MetService recorded 180 lightning strikes.

Residents report seeing blue sheet lightning - something Mr Mallinson puts down to the large magnitude of the electrical discharge.