The U.S. economy is expected to grow 2.5 percent in 2019. It noted that risks from "further disruptions in trade policies" have become more prominent.
The dominant USA economy has been shielded from the ill effects so far due to the stimulus provided through tax cuts and spending policies, but that will wear off by 2020.
The IMF, created in 1945, is an organization of 189 countries, working to foster global monetary cooperation, secure financial stability, facilitate worldwide trade, promote high employment and sustainable economic growth, and reduce poverty around the world. About half of the expected pickup in growth between 2017 and 2018 reflects the growth rebound in Nigeria.
The report warned that growth "may have peaked in some major economies".
"Owing to these changes, our worldwide growth projections for both this year and next are downgraded to 3.7 percent, 0.2 percentage point below our last assessments and the same rate achieved in 2017", the report said.
That includes President Donald Trump's imposition of tariffs on US$250 billion in Chinese goods, as well as on aluminium, steel and other products worldwide.
While the damage from an all-out trade war wouldn't be catastrophic, slow growth can also pose problems. "Mechanisms of multilateral global policy cooperation are under strain, notably in trade, and need strengthening". Separately, the International Monetary Fund predicted that the global economy would grow at 3.7 percent in 2018 and 2019, down 0.2 percentage point from its earlier estimates in July. South Africa, only 0.8 per cent this year; Angola, contracting by 0.1 per cent this year.
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"Growth is now much more uneven" than six months ago, he told reporters.
It urged the government to relax controls on its currency and to do more to help the poor to help lay the foundations for sustainable growth.
"To gauge the severity of the threats to growth, one must ask how governments could respond if risks are realised and widespread recession ensues".
India's medium-term growth prospects remain strong at 7 per cent, benefiting from ongoing structural reform, but have been marked down by just under percentage point relative to the April 2018 WEO, it said.
"Turmoil already seen in some emerging market economies could worsen, with negative spillovers to Asia through reduced capital flows and higher funding costs", it said.
"Notwithstanding the present demand momentum in the USA, we have downgraded its 2019 growth forecast, owing to the recently enacted tariffs on a wide range of imports from China and China's retaliation".
However, stimulus measures by Beijing are likely to soften the impact of the tariffs.