High tide begins to impact on beachfront homes already damaged by a weekend storm along the Pacific Ocean at Collaroy on the northern beaches of Sydney. [Photo/Agencies]

CANBERRA -- Entire towns are underwater, while at least three people are dead and many more are missing in Australia, after a vicious storm continued to batter the nation's east coast overnight.

Grave fears are held for an 81-year-old Tasmanian man, while at least three others are missing, after the worst of the weather swept across the state overnight, a day after the same storm caused wide-spread flooding and damaging king tides throughout New South Wales and the Australian Capital Territory (ACT) on Monday.

Three Australians are already confirmed dead, after a 37-year-old man was found in the Cotter River near Canberra, while two others -- a 70-year-old man and a 65-year-old man were found in New South Wales.

The devastation has caused more than 30 million US dollars'worth of damage so far, and has even prompted both Prime Minister Malcolm Turnbull and Opposition Leader Bill Shorten to suspend their election campaigns to fly to affected areas and offer support. Several towns in Tasmania remain underwater on Tuesday, while houses on the beachfronts in New South Wales face the prospect of falling into the seas, as emergency workers rush to ensure the safety of the public in affected areas.

But residents of Collaroy in New South Wales are bracing for further bad news, with the announcement that another high tide is set to smash the beachfront which has already sustained critical damage.

University of NSW coastal researcher Mitchell Harley said many homes were in "grave" danger and were falling apart under the pressure of the tide, while many had already begun falling into the sea.

Many residents have been ordered to evacuate their homes and insurance companies have been quick to declare the weather event as a "catastrophe", but have also announced that some homeowners, particularly those near the sea, might not be fully covered, meaning multi-million dollars damage bills could be left for residents to deal with.

Collaroy Beach homeowner Tony Cargorski said it was "emotional" to see his house ripped apart, while his backyard had been completely swallowed by the ocean.

"It's very emotional now to see the house like that," he said, "We got 10 to 15 meters of ground lost in the ocean. How is that going to be recovered?"

But NSW Emergency Services Minister David Elliot said it was up to home buyers to be aware of the risks of owning homes near beaches, and that they should take care when negotiating insurance policies.

"I don't know what the government can do to encourage people not to buy coastal homes," Elliot said.

"When you take out an insurance policy, make sure you know what your insurance policy covers. It's not the role of the government."