Millions of people in three states are on alert amid warnings of severe thunderstorms packing giant hailstones, heavy rain and destructive winds.

The wild weather could lash parts of NSW, Victoria and Queensland on Saturday, the Bureau of Meteorology says.

Damaging wind gusts, heavy rainfall or large hailstones are possible, forecaster Angus Hines said.

The risk was greatest in parts of northern NSW and southeastern Queensland, including Brisbane, the Sunshine Coast and Toowoomba.

"This is where we could see even more significant weather impacts in the form of giant hailstones, potentially five centimetres or greater across, and destructive winds 120 kilometres an hour or stronger," Mr Hines said.

Flash and riverine flooding, property damage, power outages, travel and transport delays

See Full Page