Destructive "tornadoes" hit Australia's northeast coast on Saturday, as officials warned parts of Queensland state to prepare for flooding, with torrential rains lashing the state set to intensify.

Queensland Premier Campbell Newman said wild gusts had caused much damage in Bargara near Bundaberg, about 300 kilometres (185 miles) north of Brisbane.

"We've had... what appears to be a mini-tornado, there are reports of significant damage," he told reporters in Brisbane.

"Unroofing of various buildings around that town, power lines down and potentially an incident where a tree has gone down on a motor vehicle with, I believe two occupants. We have declared a disaster in that area."

Police said the two people in the crushed car were seriously injured, while at least one other person was hurt by falling debris during the storm.

Bargara resident Judith McNamara told the Australian Broadcasting Corporation she saw a tree fly through the air.

"I was standing here at the kitchen and all of a sudden this big vacuum sort of came like that through here. I looked up and the next thing the tree went flying through the air, that tree and the car went up," she said.

Officials said there were also a second severe storm gust at Burnett Heads, also near Bundaberg, which damaged 150 homes.

"There are a number of small towns and suburbs that were hit by the mini-tornadoes," Queensland Emergency Services Minister Jack Dempsey said.

"We are still trying to assess the extent of the damage."

Queensland has experienced days of extremely heavy rainfall in the wake of tropical cyclone Oswald, and Newman warned that the government had concerns about potential flooding in Bundaberg and further south in Maryborough.

In Gladstone, north of Bundaberg, there are fears that flood waters could impact hundreds of properties, with some people asked to evacuate.

Newman said south east Queensland is expected to receive up to 300 millimetres of rainfall in the coming days as he warned that many beaches were closed due to high winds, high tides and dangerous surf conditions.

"The rain event has only just started, there will be more intense rain over the next two days," he said.

"Right now we are trying to get a handle on what the potential impact of those rainfall figures across the catchment will be."

Queensland experienced massive floods in early 2011 that ultimately claimed more than 30 lives, flooded thousands of homes and brought the state's capital Brisbane to a standstill, and Newman said he was aware that people were anxious.

But he said the city's dams, which were already releasing controlled discharges, would be able to absorb the current floodwaters.

"I understand that people are anxious," he said. "This is a tightrope, because I want to make sure that people have all the information but I don't want to alarm them unnecessarily. We are monitoring this very closely."