PARIS ? The world's richest countries should take immediate, tough steps to reduce debt, a "major challenge" which must be met so as to stabilize their strained public finances, the OECD said Thursday.

The 2008 global financial crisis has sent debt levels soaring as governments have spent heavily, borrowing huge amounts to try and keep their economies afloat, the Organization of Economic Cooperation and Development said.

Now their debt, averaging 100 per cent of Gross Domestic Product for the OECD members as a whole, has to come down to the much safer level of 50 per cent by 2050, it said, but that will require unpleasant sacrifices.

"In many countries, just stabilizing debt, let alone bringing it down to a sustainable level, will be a major challenge," the OECD said in a report on how member states might tackle the problem.

It said many countries will have to find savings equal to 3.0 per cent of GDP each year to bring down their debt burden but Japan, with a debt ratio of around 200 per cent, will have to cut by 12 per cent.

For the United States, Britain and New Zealand it will be more than 8.0 per cent.

After stimulus spending to tackle the 2008 crisis, many countries have switched course, driven by the eurozone debt crisis to hike taxes and cut expenditure in an effort to trim growing budget deficits.

Austerity policies may help the public finances but they also dampen growth which in turn usually cuts government income while forcing more spending on sectors such as social welfare.

The OECD recognized the problem.

"In the short term, the pace of consolidation needs to be balanced with the effects of fiscal retrenchment on growth. The trade-off will depend on the choice of (measures).

"Even so, other things being equal, slower consolidation will ultimately require more effort to meet a given debt target," it said.