Australians killed in “inland tsunami” cause by record flooding (VIDEO)

MELBOURNE, Australia — Australia's third-largest city is under threat and the nation is bracing for a heartbreaking death toll after an unprecedented flood crisis delivered its most savage blow yet: an “inland instant tsunami” that swept away everything in its path, claiming at least four lives.

The regional center of Toowoomba in Queensland state was devastated Monday by a 21-foot wall of water that continues to menace other towns in its path. Authorities said they had “grave fears” for the survival of dozens of trapped and isolated residents.

Thousands of people are being urged to evacuate to higher ground, with entire towns throughout Queensland under threat. The catastrophic flooding is also threatening to inundate Brisbane, the state's capital and Australia’s third largest city. Residents have been warned to prepare for a deluge as the Brisbane river, which runs through the city, begins to overflow.

"What we have here … is a very grim and desperate situation. This is without a doubt our darkest hour of the last fortnight,” State Premier Anna Bligh told reporters during a Monday briefing.

Declaring that "Mother Nature has unleashed something shocking,” Bligh detailed a grim list of six confirmed deaths and voiced fears for an unknown number of others. The total toll from several weeks of floods in the north-east Australian state is at least 15.

This latest unexpected disaster — coming after two weeks of flooding swamped an area described as larger than Texas and Oklahoma combined — was compounded by more wild weather and the arrival of nightfall, which made rescue efforts in remote areas difficult.

Scores, and possibly hundreds, of people were trapped in cars and on rooftops, awaiting rescue. There were unconfirmed reports of people being swept away as the buildings on which they were stranded collapsed.

In what appeared to be an attempt to prepare Australians for a potentially higher death toll by morning, Bligh and state police commissioner Bob Atkinson expressed fears for six people missing in the community of Withcott, and for another 30 people cut off — with only sporadic communication and no hope of rescue till daylight — in the tiny town of Grantham. The premier and the police chief said these official numbers represented “the bare minimum” of people in jeopardy.

The confirmed deaths included two children. A woman and her child were washed away in Toowoomba when the flash flood struck on Monday afternoon, local time. A man and a boy also drowned at the settlement of Murphy’s Creek.

Toowoomba, 80 miles west of Brisbane and with a population of about 100,000, was caught by surprise when the flood split it in two, sweeping away dozens of cars as it engulfed the town in just a few minutes. Bligh called it “a freak of nature … Toowoomba is effectively split down the center."

A city councilor, Joe Ramia, said: ‘‘I’ve lived here all my life and I’ve seen streets and football fields and ovals and school ovals that are just oceans of water. All the water ran down onto roads, into homes — just incredible.’’

In tiny Withcott, “people just can't believe what happened," said Steve Jones, the regional mayor, describing gas pumps ripped from the ground, cars swept away and houses washed from their foundations.

“Withcott's 800, 900 feet above sea level, and to be affected by floods is just something you'd never expect,” Jones told Australian Associated Press.

"At this stage we're all just a bit bamboozled by what's happened and at this stage we're trying to get them organized. There'll be some action here in the next couple of hours, but there needs to be because it is one hell of a mess."

Jones said the community had survived bush fires and would work together to overcome this latest natural disaster as well.

The bush fire comparison was apt, with the flood crisis certain to be Australia’s worst natural disaster since fires in February 2009 claimed 173 lives on a freak, bleak day memorialized as Black Saturday. The financial cost of the floods will likely exceed $1 billion, with economically vital crops and mining industries devastated by the non-stop deluge.

Ironically, Monday’s shocking escalation of the crisis came less than 24 hours after more than $10 million was raised in a nationally televised telethon that most thought signaled the transition to recovery mode. Instead, what has been described as a flood disaster of biblical scale appears to have a long way to go.

The focus now is on Tuesday’s dawn, when daylight will allow rescue efforts to resume and give authorities their first chance to assess the scale of the tragedy. Daybreak will also herald a nervous time for the 2 million people of Brisbane, where 1974 floods that claimed 14 lives are still a terrible memory for many.

Authorities said the city was inundated by a greater amount of water this time — but that they were putting their faith in vastly improved dam protection to prevent the city from being totally overwhelmed. 

Reports said Brisbane was under siege from a body of water larger than that contained in the famous Sydney Harbour, 600 miles to the south. More than 30 Brisbane suburbs have been warned to expect flooding Tuesday, with the danger expected to last well into next week. Incredibly, a king tide due on Jan. 21 — 10 days from now — might signal Queensland’s toughest day of all.