Britain's exit from the European Union would cause "a degree" of global economic uncertainty, Prime Minister Malcolm Turnbull has warned.

And he has used the prospect of an economic "shock" caused by Brexit to make the case for the re-election of the Turnbull government.

But Finance Minister Mathias Cormann has repeatedly declined to say if the federal government would pump up government spending – and potentially increase the size of the deficit – to support economic growth in Australia in the event of a global economic slowdown triggered by Brexit.