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 U.S 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."

The insurance council's Campbell Fuller said many properties on the edge of the sea are left out of policies purely because they're deemed too high of a risk.

"Many insurers don't cover actions of the sea. It's a very common exclusion," he told the Australian Broadcasting Corporation (ABC) on Tuesday.

"Actions of the sea is generally not covered by most insurance policies."

Meanwhile in Tasmania, the state's Primary Industries Minister Jeremy Rockcliff said Tuesday the fallout from the floods would be "catastrophic" for the local economy, after floods swept through the entire north of the state overnight.

"I've spoken to a number of farmers, vegetable processors and the situation for them is catastrophic," Rockcliff said.

"There are farmers who have lost 200 head of stock, dairy cattle and beef cattle. Logs have smashed through houses and irrigators have a mangled mess."

Rockcliff's comments coincide with the Tasmanian government's announcement that immediate relief aid would be provided to those affected, with up to 600 U.S dollars to be given to each family to ensure they had adequate food and water supplies.

More than 100 Tasmanians have so far been evacuated by helicopter after properties became stranded and homes were left underwater.

Authorities have said the storms are the worst to have lashed northern Tasmania since 1929, in which 22 people were killed.

Prime Minister Malcolm Turnbull took to social media overnight to urge Australians in affected areas to stay indoors and avoid crossing flooded roads, saying his government would do its best to offer support to those in need.

"Our thoughts are with all those impacted by the severe weather events around the country," Turnbull tweeted, "My government stands ready to assist and support the work of emergency personnel on the ground who have been putting their lives on the line."

"Please stay away from floodwaters, do not travel through floodwaters, stay on high ground."

The worst of the weather is said to have cleared, but the clean-up is expected to take weeks, with the damage bill expected to exceed more than 100 million U.S dollars.