In a report prepared for next week's G20 finance ministers and central bank governors meeting, the IMF says interest rates are rising as monetary policy normalises across the world economy.

It says investment incentives as part of the US tax reform package will expire and subtract from momentum, while population ageing will continue to slow productivity growth.

"The positive momentum expected for 2018 and 2019 will eventually slow, implying a challenging medium-term outlook for many countries," it says in a report released in Washington on Thursday.

It recommends economies take the opportunity to build buffers in their fiscal policy and push reforms that protect the present upswing.

It also urges central banks to keep their interest rates low where inflation remains weak.

In January, the IMF upgraded its projections for global growth to 3.9 per cent for this year and next, partly due to the more expansionary path undertaken by the US.

The Organisation for Economic Co-operation and Development made similar upward revisions this week.

The OECD also upgraded its Australian forecasts to three per cent for both 2018 and 2019.

Treasurer Scott Morrison said this was in line with where the government sees the economy going into the future because of stronger investment.

"I think that is further confirmation of the optimism and confidence the government has been expressing," he told reporters on Thursday.

The treasurer and Reserve Bank governor Philip Lowe will attend the G20 meeting in Buenos Aires on Monday and Tuesday.

Mr Morrison expects the taxation of multinationals like Google and Amazon - so-called digital taxation - will be a key talking point at the meeting, being a constant topic of conversation during his recent trip to the US.

Mr Morrison will hold a series of meetings on the sidelines of the conference, including with US Treasury Secretary Steven Mnuchin and UK Chancellor of the Exchequer Philip Hammond.

Australian Associated Press