"Several of the downside risks highlighted in the April 2018 World Economic Outlook (WEO) ... have become more pronounced or have partially materialized".
"Despite the possibility of less political space in some countries ... making consensus on sound policies often harder to reach, there won't be a better time than now for further action".
The report warned that growth "may have peaked in some major economies".
In a report released ahead of the IMF's annual conference, this year held on the Indonesian island of Bali, the fund said that the UK's "pace of fiscal consolidation can be eased if risks materialize and growth slows sharply", an outcome likely in the event of a no-deal Brexit.
It's not just the world's two most powerful economies that stand to be affected by trade policy.
The latest of these exchanges saw US President Donald Trump impose a 10 percent tariff on $200 billion (£153 billion) worth of Chinese goods in September, which would increase to 25 percent by the end of 2018.
The IMF pointed out that a full-blown trade war between the world's largest and second largest economies will cause a significant dent to the economic recovery from the Great Recession of 2018. 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.
How 'pensioner' Tito Mboweni keeps it lit on Twitter
The announcement led to a strengthening of the South African currency, the rand, which had weakened after earlier reports of Mr. She said there had been ongoing engagements between the two and that Nene had briefed him on the details around his testimony.
When the world's two biggest economies are "at odds", Obstfeld said, that is going to create "a situation where everyone is going to suffer".
It maintained a 5.3% growth forecast for the Southeast countries in 2018, but lowered the 2019 estimate slightly to 5.2%.
Fed rate hikes are already increasing pressure on emerging market economies by fuelling an outflow of capital as investors seek higher returns.
The US will also see its growth "decline" once its fiscal stimulus, delivered through wide-ranging tax cuts "goes into reverse" according to Mr Obstfeld.
Keeping rates low would avoid increasing the cost of borrowing, which could help support China's slowing growth.
Although the newly projected rate is same as last year's rate of 3.7 percent, this growth exceeds that achieved in any of the years between 2012 and 2016, and it occurs as many economies have reached or are nearing full employment and as earlier deflationary fears have dissipated.
The value of Chinese loans given to Pakistan over the last 13 months is close to the US$6.2 billion the International Monetary Fund lent it during the last bailout, according to a Bloomberg report in August.