U.S. crude oil plunged about 20 percent to below 15 U.S. dollars per barrel on Monday, hitting the lowest level in more than two decades as the COVID-19 pandemic cast a shadow of uncertainty over the global market.

West Texas Intermediate (WTI), the U.S. oil price benchmark, fell as much as 21 percent to 14.47 dollars per barrel in early Asian trading. It later pared some of those losses with a nearly 16-percent down to 15.23 dollars a barrel.

The WTI benchmark has lost about two thirds of its value since the start of this year.

International benchmark Brent crude on Monday dropped 4.2 percent to 26.91 dollars a barrel.

The oil price has been continuously falling in the past weeks as the coronavirus outbreak worldwide has frozen the global demand for the commodity and OPEC countries failed to reach a production cut deal with non-OPEC members.

Although the two sides later agreed to reduce about 10 percent of global oil supply, investors remain unsure whether the cut could offset the plummeting demand as many cities are locked down and trade has been largely restricted to contain the virus's spread.

With the slowdown of COVID-19 cases in some European countries including Germany, Austria and the Czech Republic, the authorities have considered gradually withdrawing the restriction measures.