Prime Minister Julia Gillard has pledged to provide Queensland with whatever support it needs from the Australian Defence Force to cope with the floods in the south-east of the state.
Flash floods in the city of Toowoomba, west of Brisbane, killed at least 10 people on Monday. Ninety more people are missing. Brisbane and Ipswich are now threatened.
Ms Gillard has warned there were still "dark days ahead".
"The nation does need to brace itself for the fact that the death toll as a result of yesterday's flash flooding and walls of water is likely to rise," she said in Canberra on Tuesday before leaving for Brisbane.
Ms Gillard offered her sympathies to the families and friends of those who had lost loved ones.
"To those people who are bereaved, to those who are now waiting for news of their loved ones, I want to say to them as prime minister my thoughts and my sympathies are with you," she said.
"The thoughts and sympathies of all Australians are with you in these dreadful and difficult circumstances."
Ms Gillard said she had been briefed by Australia's national security adviser as well as the head of Emergency Management Australia.
She has also spoken to the commanding officer of Operation Queensland Flood Assist.
"We have helicopters - Blackhawks and Sea Kings - in the air working hand in glove with the Queensland emergency personnel on search and rescue efforts."
Ms Gillard described the circumstances in Queensland as "very dire indeed".
"There are some communities that have been hit by floodwaters for a second time - hit once, evacuated, gone back, and now being hit again."
The government would continue to provide support from the Australian Defence Force.
"And I have made it very clear to Premier Anna Bligh that any resource she needs from the Australian Defence Force will be made available to the people of Queensland to assist them during this very difficult period."
The prime minister also praised the courage and commitment of emergency services personnel who had faced "incredibly harrowing circumstances" during the past 24 hours.
"I thank you for what you have done, what you are continuing to do and what you will do in the days ahead."
Ms Gillard said there were "still more dark days ahead ... but the spirit of Queensland is to face these circumstances with courage and determination."
She also confirmed offers of help had been received from other countries.
Defence Minister Stephen Smith said the ADF would deploy additional helicopters.
Three army Black Hawk helicopters, two Navy Sea King helicopters, an Army CH47 Chinook helicopter, two RAAF B350 King Air planes and an RAAF C-130 Hercules are already involved.
The Black Hawks were used in the evacuation of the entire town of Forest Hill, 80km west of Brisbane, which is floodbound.
Ms Gillard's office says there is no military assistance from New Zealand in Brisbane.
Ms Gillard was earlier quoted as saying an offer of offer of military support by New Zealand was the first overseas offer to be accepted.
But a spokesperson for Ms Gillard says the prime minister was referring to New Zealand's Civil Defence deployment which is already assisting the flood crisis in Queensland.