Prime Minister Julia Gillard said there had been a "terrible loss of life and suffering" as she extended her deepest sympathies to those affected.
"Australians have watched these tragic events with sheer disbelief, particularly in light of the events we saw in our own backyard over our summer," she said in reference to deadly floods and destructive cyclone Yasi.
"The government today offered to support the United States in any way possible as severe tornadoes claimed hundreds of lives across the southern part of the country," she said in a statement released late Saturday.
Foreign Minister Kevin Rudd said Australians, who saw more than 30 people killed in massive floods which covered an area of Queensland state the size of France and Germany combined, empathised with America's suffering.
"The United States is one of our closest friends and we are always there for each other," he said in the joint statement.
The powerful tornadoes in the southern United States killed close to 350 people, making the storm the second-deadliest tornado-related tragedy in US history. The worst tornado outbreak in the country killed 747 people in 1925.