U.S.-China tariffs, that have been both implemented and proposed, could cut global economic output by 0.5% in 2020, the International Monetary Fund (IMF) warned Wednesday.

Christine Lagarde, the IMF's managing director, said in a briefing note for G-20 finance ministers and central bank governors that taxing all trade between the world's two largest economies would cause some $455 billion in gross domestic product to evaporate. This would be a loss larger than South Africa's economy, it said.

"There are growing concerns over the impact of the current trade tensions. The risk is that the most recent U.S.-China tariffs could further reduce investment, productivity, and growth. The just proposed U.S. tariffs on Mexico are also of concern," Lagarde said in the blogpost.

"Indeed, there is strong evidence that the United States, China, and the world economy are the losers from the current trade tensions," she added.

Lagarde on Wednesday called them "self-inflicted wounds" that must be avoided "by removing the recently implemented trade barriers and by avoiding further barriers in whatever form."

In July last year, President Donald Trump indicated that he was willing to slap tariffs on every Chinese good imported to the U.S. should the need arise. "I'm ready to go to 500," the president told CNBC's Joe Kernen.