Australians were holding a national day of mourning for the 173 people who died a year earlier in the country's worst wildfire disaster.

Prime Minister Kevin Rudd planned to attend a church ceremony in the southern city of Melbourne, and smaller gatherings were held in hamlets that were wiped out by the infernos in Victoria state on what is now called Black Saturday.

Hundreds of fires raged across the state as temperatures soared and powerful winds whipped blazes into firestorms. By the end of the day, 173 people were dead and more than 7,000 homes razed.

"The loss of so many men, women and children was almost too much to bear and their absence still weighs heavily on their communities and all of those who loved them," Victoria premier John Brumby said in a condolence message.

The government ordered flags to be lowered to half mast around the country, and commemoration services were broadcast nationally on television and radio.

At Marysville, where most houses were gutted by fire and 34 people died, survivors gathered at a sports field that became a lifesaving refuge for many as flames roared all around them on Black Saturday. Green shoots of new growth sprung from many eucalyptus trees surrounding the field, though their trunks were still charred black.

Australia endures hundreds of wildfires every summer season, many caused by lightning strikes, sparks from machinery or other human activity -- and some by arsonists. Thousands of acres of forest and farmland are left charred, and deaths regularly occur.

But disasters on the scale of Black Saturday are rare and it deeply shocked the country.

A quasi-judicial inquiry is still under way into the causes of the disaster and the effectiveness of the authorities' response. Preliminary findings found communications and other failures hampered efforts to fight the fires, and prompted changes to laws and new procedures to try to cope with future events.

Officials have also toughened warnings to residents in fire-prone areas about choosing whether to stay with their homes and defend them or to leave early for safe havens. Some of those who died on Black Saturday were killed in their cars or on foot after waiting until too late to flee.