WA Treasurer Mike Nahan has blamed a "perfect storm" for the $3.1 billion 2015-16 deficit blow out announced on Monday, as part of the state government's mid-year review of the state budget.

Dr Nahan said a combination of falling commodity prices, a softer domestic economy and WA's reduced GST share had hit revenue forecasts hard, resulting in a revised $17 billion deficit for the four-year, 2014-15 to 2018-19 budget.

WA's deficit has blown out to $3 billion, Premier Colin Barnett has announced. Credit:Aaron Bunch

"It is the biggest cut to revenue any government has seen since the 1920s great depression," he said.

"We're still growing, less than we were but we're still growing... but the revenue shock to Western Australia has been profound.