THE OPPOSITION finance spokesman, Barnaby Joyce, believes the United States government could default on its debt, triggering an ''economic Armageddon'' which will make the recent global financial crisis pale into insignificance.

Senator Joyce said yesterday he did not mean to alarm the public but there needed to be a debate about Australia's ''contingency plan'' for a sovereign debt default by the US or even by a local state government.

Armageddon warning ... Barnaby Joyce. Credit:Pat Scala

''A default by the US means complete economic collapse around the world and the question we have got to ask ourselves is where are we in that,'' Senator Joyce said.

His warning came as the Rudd Government ramped up its attack on Senator Joyce as an economic extremist by highlighting his strong opposition to Chinese sovereign investment in Australia.