Flood not expected to hit homes: BOM

Queenslanders have been reassured their homes are unlikely to be inundated, despite rising river levels in the state's southeast.

However, the Bureau of Meteorology says it cannot rule out the possibility as Cyclone Marcia tracks south.

Flood warnings have been issued for several areas including the upper Brisbane River, Somerset Dam around Woodford, the Maroochy and Mooloolah river systems, and Gympie.

BOM spokesman Jess Carey said heavy rainfall is expected to continue overnight, driving up water levels in the river systems of Brisbane, Logan and the Gold Coast.

Mr Carey said it was too early to tell how high the water would rise or whether homes would be affected.

"We really need to see the rainfall on the ground first," he told AAP.

"The largest potential really in terms of flood effects will probably be roads being closed and potentially bridges going under.

"What we wouldn't be looking at right now is inundation of people's properties. That's certainly not in the ballpark at the moment.

"That's not to say it's not possible."

Cyclone Marcia crossed the coast north of Yeppoon on Friday morning and is expected to weaken as it moves south-southeast during the next two days.

Rain drenching the southeast corner is being generated by a separate trough, which is being fed by Cyclone Marcia.

On Saturday, the southeast will begin to feel the full effects of Marcia, though the category three cyclone is expected to weaken to a tropical low about noon.

Gympie is forecast to be hardest hit by flooding in the southeast, with the Mary River level predicted to reach 12m.

Gympie Regional Council spokeswoman Rae Gâté said the town's centre would not be affected until levels reached 18m.

Seqwater has warned residents downstream of Borumba Dam, south of Gympie, and Wyaralong Dam near Beaudesert that outflows have reached levels that could be dangerous.