The Defence Department’s acting chief says it could take five years to ramp up defence spending to an additional $40 billion a year, while Australia’s top military commander warned of war waged from Australia’s shores.

Matt Yannopoulos, acting secretary of the Defence Department, said he was not surprised the US was calling for Australia to lift defence spending from about 2 per cent of the economy to 3.5 per cent, given it had been making similar calls around the world. But when asked on Wednesday if it was possible, he said not immediately.