"If we put all this together, we see global growth that is disappointing and uneven. In addition, medium-term growth prospects have become weaker," she said. "The 'new mediocre' of which I warned exactly a year ago — the risk of low growth for a long time — looms closer."
On China, Lagarde said she sees Asia's largest economy as undergoing a fundamental and welcome transformation. The IMF head warned that this sort of transition can create "spillover effects" in trade, exchange rates, asset markets and capital flows.
Read MoreWeak productivity growth hits global economy: WEF
China will likely reduce its appetite for commodities as its economy slows and the country invests less overall, Lagarde explained in her speech. "This will contribute to what could be a prolonged period of low commodity prices — a change that will need to be managed by policymakers, particularly in the large commodity exporters," she said.
In fact, Lagarde told CNBC that she expects emerging markets will likely see more volatility ahead.
As for the Federal Reserve, Lagarde said she was encouraged by how the U.S. central bank is going about its decision-making on when to raise rates.
Read MoreYellen: Rate hike path more important than timing
"We are very pleased to see the fact that the decision will be data dependent — we think that that's very, very good. We don't see much movement on the inflation front nor on the wages front, so we are also very interested to see that the international scene is also perceived as likely to have domestic effects and may have been factored into the thinking," she said, adding that her organization does not see an economy ready for a rate hike.
The World Trade Organization announced that it had cut its forecasts for global goods trade earlier Wednesday after quarterly growth turned negative, with trade shrinking by an average of 0.7 percent in the first two quarters of this year. The WTO said it sees world trade growth of 2.8 percent this year and 3.9 percent in 2016, revised down from the forecasts it made in April of 3.3 percent and 4.0 percent, respectively.
—Reuters contributed to this report.