Some areas of Sydney are set for "catastrophic" conditions on Saturday, and the deadly fires are now engulfing other parts of the country. One person was killed in a car crash on Friday near South Australia's capital city of Adelaide, where an emergency warning is in place though the precise circumstances surrounding the death is not yet clear.
Australia has been fighting wildfires across three states for weeks, with blazes destroying more than 700 homes and nearly 3 million acres (1.2 million hectares) of bushland.
The death of the two firefighters overnight, when their fire truck was struck by a falling tree as it traveled through the front line of a fire, brought the fires death toll in New South Wales to eight since the beginning of October.
Ten more firefighters were seriously injured on Thursday, with four in South Australia being treated for burns and smoke inhalation.
"The worst imaginable set of circumstances unfolded," New South Wales (NSW) Rural Fire Service (RFS) Commissioner, Shane Fitzsimmons, told reporters in Sydney. "This hurts everybody to the core."
Shortly after the pair's deaths were announced, Morrison issued a statement saying he would return as soon as possible from a family holiday in Hawaii, a trip that has drawn sharp criticism in recent days as the wildfires crisis deepened.