Policy analysts and aid groups say the Australian Opposition's foreign aid cuts will have a significant and immediate impact on the effectiveness of the nation's aid program if it wins tomorrow's election.

The Coalition on Thursday revealed its costings, less than 48 hours out from the poll.

They include slashing the growth rate of foreign aid spending, saving $4.5 billion over four years.

The Coalition is yet to reveal which foreign aid projects will be affected.

More than seventy per cent of Australian's foreign aid is spent in the Asia Pacific region.

Key points: Coalition says its figures would improve budget bottom line by $6 billion.

Coalition says its figures would improve budget bottom line by $6 billion. Extra $1 billion would be seen as a result of an increased economic activity after scrapping of carbon tax.

Extra $1 billion would be seen as a result of an increased economic activity after scrapping of carbon tax. A reduction in government debt by $16 billion.

A reduction in government debt by $16 billion. Extra $5 billion over forward estimates for key infrastructure projects.

Extra $5 billion over forward estimates for key infrastructure projects. Infrastructure projects to be paid for by $4.5 billion cut to foreign aid.

Infrastructure projects to be paid for by $4.5 billion cut to foreign aid. Re-phase $650 million of Murray-Darling Basin water buy-back programs.

Australian aid spending is currently at 0.37 per cent of national income or 37 cents in every $100.

World Vision forecasts that the cuts foreshadowed by the Coalition will take the aid budget down to around 0.33 per cent of national income over the four-year forward estimates.

UNICEF Australia's chief executive, Norman Gillespie says news of the foreign aid cuts came as a surprise.

"This has come as quite a shock, the size of it, the scale of it and simply the giving up of the principle of a civilised nation helping those who are in extreme poverty and in need," he said.

Oxfam Australia Chief Executive Dr Helen Szoke says the cut is at the expense of the world's most vulnerable.

"We know for example that still 1 in 8 people go to bed hungry every night," she said.

"There's still a job to be done and what we were hoping was that with a bipartisan commitment we'd be able to continue the momentum to actually doing that job and that will now be slowed down."

Dr Szoke says the cut exacerbates the Labor government's delayed introduction of a commitment to spend 50 cents in every $100 of revenue on aid.

She says it will affect successful aid initiatives.

"In any one year there will be over 2 million children who will be vaccinated, there will be 2 million people who will have access to safe water, there will be over 1 million children enrolled in schools," she said.

"If you think about if that slowed that down then you can kind of see the knock on effect of that change."

Sorry, this video has expired Joe Hockey, Andrew Robb reveal costings

The Foreign Affairs Minister Bob Carr says it's against Australia's interests to further cut spending on foreign aid.

Labor has already reduced the growth in foreign aid spending.

Senator Carr says much of the money is spent on overseas programs that indirectly benefit Australia.

"It's in our interests, Australia's security is served by an effectively delivered foreign aid program and it's a false proposition to say we only provide infrastructure for Australian cities by hacking into foreign aid' Senator carr said.

Professor Stephen Howes from the Australian National University's Development Policy Centre told Pacific Beat little detail about the cuts will harm the ability of AusAID and NGOs to implements Australian aid.

"To cut the aid budget in the current year when budgets have been drawn up, plans mave been made... we know the aid program is fully committed," he said.

"In fact the aid program is under additional stress because of the new deal with Papua New Guinea, so I think it is going to be very damaging to the effectiveness of the aid program to have to rip $600 million out of it."

Mr Howes says NGO's will suffer despite assurances of further funding from the Opposition Treasury spokesman, Joe Hockey.

"Joe Hockey said that NGOs are going to receive additional funding but I think the entire aid sector which has experienced strong growth over the last decade is now going to be in for a pretty tough time," he said.

"That will start with AusAID but the ramifications will be felt well beyond AusAID and despite the assurances of Joe Hockey it's hard to see how NGOs will escape."

Money for roads

Sorry, this video has expired Australian Opposition plans to cut foreign aid ( Catherine McGrath )

The Coalition plans to redirect foreign aid money into roads.

Its Treasury spokesman Joe Hockey says Australia can only be a more generous nation to the rest of the world if it has a strong economy.

"We can't continue to fund a massive increase in foreign aid at the expense of investment in the Australian economy to get the Australian economy to grow at trend and hopefully above trend growth," he said.

"So we have to cut the growth in foreign aid to fund Australian infrastructure, because the stronger the Australian economy, the more generous we can be in the future."

Greens leader Christine Milne says cutting foreign aid in order to boost infrastructure in Australia is disgraceful.

"To say that we would support infrastructure in Australia at the expense of the world's poorest people is shocking to behold," she said.

"The very idea that we live in the Asia Pacific region, where two thirds of the world's poor live - the geopolitics of this century are going to be dominated by our region.

"We talk all the time about the need for building greater cooperation in the Asia Pacific region and how do we behave? We slash our commitment to foreign aid."

Australian National University policy analyst Professor Stephen Howes says putting money into roads at the expense of foreign aid is not an argument many Australian voters will readily accept.

"Aid is not a big election issue for most Australians," he said.

"There are a number of campaigning groups, especially youth groups for whom it is a big issue, but I think even for those who are not strong supporters of aid, I don't think people will buy the argument we're going to cut our aid budget so that we can build more roads."

Aid organisations say the Coalition's foreign aid cuts would make Australia's commitment to reducing world poverty under the Millennium Development Goals non-existent.

The aid sector has accused the Coalition of balancing the budget on the back of the world's poor.

World Vision Australia's chief executive Tim Costello received news of the cuts at the G20 meeting in St Petersburg in Russia.

"I'm pretty devastated by this because the truth is we are one of the few G20 nations here still growing and our first act, as assuming the presidency, is to cut aid," he told PM.

"This isolationist sort of policy seems to think Australia's an island.

"The actual levers, as we see here at the G20, are global and aid is so fundamental to dealing with health and education if you're going to have trade and an open growing global system that I think is really unwise."