Angel Gurria, secretary-general of the OECD Jose, addresses the media at the organization's headquarters in Paris, France on Nov. 21, 2018.

Roughly a decade after the global financial crisis, central banks around the world may not have much left in their toolkit to boost the economy, according to the head of the Organisation for Economic Co-operation and Development.

Angel Gurria, OECD Secretary-General, made that comment on Friday as major central banks such as the U.S. Federal Reserve and the European Central Bank recently signaled their readiness to cut interest rates. That dovish turn came amid an ongoing trade war between the U.S. and China — which many economists have warned could derail an already slowing global economy.

Gurria told CNBC's Nancy Hungerford that the world "would be much worse off today" without central banks working to stimulate economic activity in the past decade. However, central banks "have run out of ammunition," he said.

"Interest rates are at zero practically everywhere, or very close. And now we know interest rates are going to remain low for longer, that is as much as the central banks can do," he said at the G-20 summit in Osaka, Japan.

He added that it's time fiscal policies play a bigger part in boosting economic activity. That means countries that can afford to spend more without jeopardizing their finances should do so, he explained.

"Some countries, of course, are taking care of their debt. But some countries do have capacity to actually spend more in a controlled fashion," he said. "So, coordinated fiscal policy is the next stage."