Australia braces for catastrophic wildfire day By Rob Taylor CANBERRA (Reuters) - Australia was bracing on Monday for days of "catastrophic" fire and heatwave conditions, with fires already burning in five states and as a search continued for people missing after devastating wildfires in the island state of Tasmania. Prime Minister Julia Gillard toured fire-ravaged Tasmanian townships and promised emergency aid for survivors, who told of a "fireball" that engulfed communities across the thinly-populated state on Friday and Saturday. "The trees just exploded," local man Ashley Zanol told Australian radio, recounting a wall of flames that surrounded his truck as he carted water to assist fire crews in the hard-hit township of Murdunna, largely leveled in the inferno. Tasmanian police said around 100 people feared missing in bushfires had been accounted for and there had so far been no deaths as authorities combed through still-smoldering ruins of homes and vehicles, while evacuating local people and tourists. Bushfires were ablaze in five of Australia's six states, with 90 fires in the most populous state New South Wales, and in mountain forests around the national capital Canberra. Severe fire conditions were forecast for Tuesday, replicating those of 2009, when "Black Saturday" wildfires in Victoria state killed 173 people and caused $4.4 billion worth of damage. A record heatwave, which began in Western Australia on December 27 and lasted eight days, was the fiercest in more than 80 years in that state and has spread east across the nation, making it the widest-ranging heatwave in more than a decade, according to the Australian Bureau of Meteorology. Tuesday would bring the highest "catastrophic" bushfire temperature conditions, said fire officials, under which people are advised to flee if fire threatens, as the blaze is likely to be too fierce for fire crews to easily extinguish. "Any fire that burns under the predicted conditions -- 40 degree (Celsius) temperatures (104 Fahrenheit), below 10 percent humidity, winds gusting over 70 kilometers an hour (43mph) -- those conditions are by any measure horrendous," said New South Wales Rural Fire Service Deputy Commissioner Rob Rogers. In the Australian capital Canberra, hit by a firestorm in 2003 that destroyed hundreds of homes, authorities said they were expecting the worst conditions in the decade since, with a fifth day of searing temperatures and strong winds. "With those winds it boosts up the fire danger significantly," the city's deputy fire chief Michael Joyce told local reporters. Blazes sparked by weekend lightning storms were already burning in forests surrounding the sprawling lake-and-bushland city, as they did 10 years earlier. Australia, the world's driest inhabited continent, is particularly vulnerable to bushfires, fuelled each summer by extreme heat and by what climate scientists say is creeping climate shift blamed for hotter average temperatures globally. Authorities warned earlier in the Australian summer that much of the country faced extreme fire conditions this season, after several years of cooler conditions that had aided forest growth, but also created tinder dry fire fuel conditions. Gillard warned all Australians to be alert as temperatures soared in coming days. "We live in a country that is hot and dry, and where we sustain very destructive fires periodically, so there is always going to be risk," she told reporters. We do know over time that as a result of climate change we are going to see more extreme weather events and conditions. Australia is the world's second largest wheat exporter, but it's wheat harvest was not expected to be affected by the fires and hot weather, as the vast majority of this season's winter crop had already been harvested, analysts said. "In respect to the summer crop, the sunflowers, sorghum for example, the weather will have an impact, particularly in northern New South Wales where they had low soil moisture coming into the season," said Andrew Woodhouse, grains analyst at Advance Trading Australasia. GrainCorp, Australia's largest listed agricultural company, said the planting window for crops like sorghum closes in mid-February, which would allow farmers to delay seeding until conditions improve. "Farmers will be looking for rain for sure, but we will have to wait and see what happens," said GrainCorp spokesman Angus Trigg. Additional reporting by Colin Packham; Editing by Michael Perry