Australia declared a national emergency on Wednesday in response to devastating floods along its east coast, and designated catastrophe zones in towns swept away by swollen rivers.

“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, kept media away from his meetings with flood victims, which he said was to protect their privacy.

Television footage showed some people gathered in front of an emergency operations centre Morrison visited, yelling “the water is rising, no more compromising” and “fossil fuel floods”.

Morrison’s conservative government late last year adopted a net zero carbon emissions target by 2050, but climate activists are demanding more aggressive action.

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.

Officials said military personnel deployed to the region to assist the cleanup operations would be more than doubled to 4,000.

The government has paid out some A$385 million to flood victims nationally in the past week, and Morrison said aid would be increased in Lismore, of the hardest hit towns, and surrounding areas, to provide food and shelter, mental health support and legal and business support.