American authorities announced on Sunday an emergency authorization for doctors to use blood plasma from recovered coronavirus patients as a treatment against the disease that has killed over 176,000 in the US.

The move by the Food and Drug Administration comes as President Donald Trump faces intense pressure to curb the contagion that has hobbled the world's largest economy and clouded his once-promising prospects for re-election in November.

The plasma is believed to contain powerful antibodies that can help fight off the disease faster and help protect people from being seriously hurt by it.

"This product may be effective in treating COVID-19 and... the known and potential benefits of the product outweigh the known and potential risks of the product," FDA said in a statement.

While the treatment has already been used on patients in the United States and other nations, the extent of its effectiveness is still debated by experts and some have warned that it could carry side effects.

"Convalescent plasma probably works—though it still needs to be proven in clinical trials—but not as a rescue treatment for people who are already severely ill," said Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City.

Trump faces tough campaign

He said that plasma would likely work much better right after a person was exposed to the virus, when the body is trying to neutralize the infection—the problem being that plasma supplies are limited, meaning it would be difficult to get enough to treat everyone in early stages of the disease.

Trump told reporters the therapy shows "an incredible rate of success" and "will save countless lives", but this went much further than his own health officials' cautious welcome of the treatment.

Challenged by a reporter to explain the apparent contradiction, Trump passed the question to one of his experts, then ended the press conference.

The FDA already allowed convalescent plasma transfusions for coronavirus patients under certain conditions, such as clinical trials and gravely ill people.

The Washington Post said that over 70,000 virus patients in the US have received such a transfusion.

Trump has been widely criticized for his handling of the coronavirus pandemic in the US, which remains the world leader in infections and fatalities.

He faces a tough re-election battle against Democratic challenger Joe Biden, with no effective treatment or vaccine expected before the vote on November 3.