MELBOURNE: Widespread flash floods unleashed by heavy rain in Australia's northeastern state of Queensland have killed two people, including an emergency services volunteer, officials said on Saturday, taking the death toll to four.

Weather officials warned of a major flood, with severe storms expected to persist into Sunday, threatening to push waters in the state's major Mary river system beyond a level of 21.95 m (72 ft) not seen since 1999.

"This is going to exceed an event that hasn't happened in at least 20 to 25 years," Bureau of Meteorology forecaster David Grant told a briefing.

Two people were reported missing in the floodwaters.

"This is a very intense and dangerous weather system sitting over southeast Queensland at the moment," Greg Leach, head of the state's fire and emergency services, told the Australian Broadcasting Corporation (ABC).

"There is no sign of it easing up."

The volunteer died when flood waters swept off the road a car in which an emergency team was responding to a call for help, but three other occupants were rescued, he said.

"Tragic news for us overnight with the loss," Leach added.

A body retrieved from floodwaters in the capital of Brisbane accounted for Friday's other death.