That is the warning in a report from economists at the World Bank.
But there are some more upbeat aspects of their assessment. They don't reject the idea that this might just be a temporary soft patch.
And they say emerging economies are not as vulnerable as they were in previous decades.
The starting point for this report is the marked slowdown in growth that has already taken place in the emerging market economies since 2010.
They have grown more slowly than the five years before the international financial crisis. By last year, the growth rate had slipped below the long-term average.
China is the most high-profile example and in a way it's a special case. A slowdown there was seen as inevitable after three decade of rapid economic expansion.
But many others in this group have also seen their performance weaken including Brazil, Russia and South Africa. (India is something of an exception.)
Their slowdown contrasts with a weak but steady recovery in the advanced economies.
The central question posed by the report is whether this is a temporary problem or the beginning of a new era of slower growth.
There is no definitive answer in this report, but there is a clear sense of unease that it might be the latter, less attractive of the two possibilities.
Some of the factors behind the slowdown are likely to be persistent. Many are affected by sliding prices of commodities such as metals and oil. There has also been weaker demand in export markets for their products, which in turn partly reflects what the report calls "anaemic growth in the advanced economies".
International trade is likely to stay weak as the rich countries' recovery remains hesitant. Large investments in commodity production in recent years are likely to mean strong supplies which will keep downward pressure on prices.
Some, especially oil exporters, have seen a deterioration in government finances as tax revenue has fallen sharply.
There also been a marked decline in foreign investment going into emerging economies. It fell by about a quarter between 2010 and 2014. In the first part of 2015 there was a marked increase in capital leaving the emerging economies.
There are also domestic factors, including aging populations in many emerging economies.  The growth in productivity - the amount that each worker produces - has slowed in many.
The report describes the slowdown as "unusually synchronous (affecting many countries at the same time) and protracted".
Looking, ahead the report notes the prospect of higher borrowing costs as the US Federal Reserve is expected to start raising interest rates - widely expected to begin as soon as next week.
That is likely to lead also to a stronger dollar. That makes money borrowed in dollars more expensive to repay and the amount of foreign currency debt has increased from 30% of emerging economies' national income in 2007 to 36% last year.
Declining currencies could also cause an inflation problem - they make imports more costly.
There are clearly some reasons to be concerned. But the World Bank's economists also emphasise how these countries have changed compared with the 1980s and 90s.
They have reduced debt and inflation levels, diversified their economies (they are less dependent on specific industries and so less in danger if those industries get into difficulty). And they have improved their economic policies.
What should they do? There is no one-size-fits-all. Those who can afford to spend more on infrastructure (transport, telecommunications, energy) would benefit from doing so.
There's a call for continued efforts to improve the climate for business, make labour markets more effective, tackle corruption and improve the efficiency of government.  Much of this is frankly advice the Bank would give to most countries most of the time.
So no hard conclusions here.  More of a warning; a call for economic vigilance.

The world number 324, who represented Australia until 2013, swept through the first set against the Argentine.
Find out how to get into tennis in our special guide.
The 27-year-old Briton then wasted four match points in the second set tie-break as Bagnis hit back to level.
But Klein retained his composure and overturned a 5-2 deficit in the final set to win the match in the tie-break.
Klein will play Portugal's Joao Sousa in the second round.
The emerging market countries are at a crossroads, facing the possibility of new era of slower economic growth.
[NEXT_CONCEPT]
Briton Brydan Klein reached the second round of the Auckland Open with a 6-1 6-7 (6-8) 7-6 (7-3) win over Facundo Bagnis - ranked 269 places above him.