A 20-year-old Brisbane man died after he was swept away in a stormwater drain during Queensland's worst storms in 25 years.

Police believed the man and a 23-year-old companion were taking photographs in a drain near Westfield Shopping Centre at Chermside when the water suddenly rose, sweeping them away.

Police and the QFRS Swift Water Rescue Team plucked the 23-year-old man out of the drain after he managed to grab hold of a grate.

But the 20-year-old was swept away. His body was found a few hours later, police said.

'War zones'

Some Brisbane suburbs have been described as war zones this morning after the storms swept through the state's south-east last night.

Reports from The Gap, which was one of the worst hit areas, are that significant amounts of debris, including large trees, are scattered over a wide area and across several roads.

Police appealed for patience from commuters after widespread power outages knocked out traffic lights and debris blocked many roads.

A freight train blocked the McKean Street Rail crossing at Caboolture at the Beerburrum Road end. The Ferny Grove train line was cut due to tree branches across the tracks.

The thunderstorms carved a swathe of destruction from the Gold Coast hinterland through to Brisbane and the Sunshine Coast with up to 230,000 homes reportedly losing power across the state's south-east.

Dams boosted by heavy rain

The rain has provided Brisbane with an extra three to four days of water supply. Combined dam capacity increased by 0.08 per cent after the storms.

Somerset Dam rose by 24mm and North Pine Dam by 32mm - the largest inflow for both dams in the past two and a half months.

Dam levels are expected to increase over the week with more heavy rain forecast.

brisbanetimes.com.au and AAP