PERTH: Australian Prime Minister Malcolm Turnbull on Saturday announced more than a dozen changes to his ministry, the second major reshuffle in the five months he has been leader and ahead of national elections expected later this year.

Turnbull was forced into the major cabinet reshuffle by the resignation of one minister, the retirement of two long-standing senior ministers and the sacking of two others over their involvement in political scandals.

The new cabinet lineup represents "a dynamic team which combines youth, new talent, experience, continuity, and a real sense of innovation and enterprise", Turnbull told a news conference in Sydney.

"Change offers opportunity...there comes a time when you need to transition from older leadership to newer leadership. Turnover, change, is good...is is a revitalised government and it is revitalised because of new blood coming in," he said.

Turnbull's Liberal-National coalition is the frontrunner to win elections expected in October - his first poll as Liberal party leader and prime minister. A victory would secure Turnbull a popular mandate and secure his position as party leader.

Turnbull ousted former Liberal leader Tony Abbott in a leadership coup last September and is under pressure to unite his divided government.

The retirement of Australia's deputy prime minister on Thursday saw Turnbull inherit a National party political rival, hard-right, climate change sceptic as his deputy, an appointment that could block any revamp of an emissions trading scheme and give farmers a greater say in government policy.

Agriculture Minister Barnaby Joyce became deputy prime minister when he was voted to lead the coalition's minor partner, the Nationals.

Turnbull appointed eight new ministers and boosted the number of women in his cabinet from five to six on Saturday.

The major change sees Australia's trade minister Andrew Robb, who led negotiations for landmark free trade agreements with China, Japan and Korea and the multinational Trans-Pacific Partnership, become a special trade envoy. He will be replaced as trade minister by Steven Ciobo.

Australia is in the midst of several trade negotiations, including free trade deals with India and Singapore.

The coalition government won a landslide election in 2013 but Abbott saw his popularity plummet in the wake of a hugely unpopular 2014 austerity budget.

Plummeting commodity prices have depleted the government's coffers, a major financial stumbling block for Turnbull, whose rise was sparked partly by his image as a prudent financial manager based on his background in the private sector.

Australia in December forecast its budget deficit would swell to A$37.4 billion ($26.48 billion) in the year to June as falling prices for key resource exports open a gaping hole in tax revenue.