The federal budget will remain in deficit for the foreseeable future and the government will not focus on a return to surplus and stabilising debt until the unemployment rate is "comfortably'' below 6 per cent, Treasurer Josh Frydenberg says.

The budget to be released on October 6 is expected to forecast gross debt to exceed 45 per cent of GDP, pushing it close to or over $1 trillion, while the deficit for this financial year is expected to be above $200 billion. Deficits will be forecast for the subsequent three years as well.