Australian military aircraft and vessels will be deployed to help emergency services in the fire-ravaged states of New South Wales (NSW) and Victoria.

Thousands of people fled to beaches in the south-eastern states on Tuesday as emergency-level fires spread.

In Mallacoota, Victoria, about 4,000 people sought shelter on the coast.

Two more people have been confirmed dead in NSW, bringing the fire-linked death toll to 12.

Authorities say four people are missing in Victoria and another in NSW.