Australia declared a national emergency on Wednesday as devastating floods wreaked havoc along its east coast and portions of some towns were swept away.

Officials said military personnel deployed to the region to assist the clean-up operations would be more than doubled to 4,000, according to a Reuters report.

"Australia is becoming a harder country to live in because of these natural disasters," Prime Minister Scott Morrison said on Wednesday after touring the worst-hit Northern Rivers area of New South Wales.

The emergency declaration, which was set up after Australia's destructive 2019 bushfires, will help cut red tape and speed up aid amid criticism about a slow response to the floods in which at least 21 people have died.

Frustrated residents in the Northern Rivers, with no access to power and internet for several days, have blamed authorities for the slow speed and scale of relief efforts.

Morrison, who is trailing in polls ahead of a federal election before May, announced that flood victims will be given “immediate” tax relief and up to $3000 in emergency payments in a federal pledge to intensify support after Prime Minister Scott Morrison had to apologise to communities in northern New South Wales, according to a report in the Sydney Morning Herald.

With Labor accusing Mr Morrison of bungling his response to the floods, the government raced to offer more assistance in a political fight over competence ahead of the federal election.

Speaking to reporters, Morrison linked the devastation to climate change, which he said had also caused earlier bush fire catastrophes, but he went on to say the greater challenge was reducing other countries' emissions.

What will save people is flood mitigation works, rather than tougher curbs on Australia's emissions, he said.

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