Melbourne has been issued with a severe thunderstorm warning by the Bureau of Meteorology for at least the next hour.

The thunderstorms were detected at 3.45pm and are due to sweep across the city, said the Bureau. Damaging winds are likely, with a wind gust of 90km/h already observed at Laverton.

The State Emergency Service is warning people to keep clear of fallen power lines, stay indoors if possible, avoid using the telephone, avoid sheltering under trees and switch off computers and electrical appliances.

Another thunderstorm warning may be issued by 4:55 pm.