WASHINGTON: The United States announced an emergency authorization to use blood plasma from recovered coronavirus patients as a treatment for the disease, which has killed more than 800,000 people around the world. Many governments around the world are renewing efforts - including the reimposition of lockdowns - to contain the virus, which has infected well over 24 million people.

The United States remains the hardest-hit country with more than 176,000 fatalities, and President Donald Trump is under intense pressure to curb the contagion. The plasma therapy shows "an incredible rate of success" and "will save countless lives", Trump claimed on Sunday - but that went much further than his own health officials' cautious welcome of the treatment.

Plasma is believed to contain powerful antibodies that can help fight COVID-19 faster, and has already been used on patients in the United States and other countries. But the extent of its effectiveness is still being debated by experts and some have warned it could carry side effects.

When challenged by a reporter to explain the contradiction between his confidence in the treatment and the caution among experts, Trump passed the question to one of his experts and then ended the press conference. Trump will attempt to galvanize support at the Republican convention, which starts Monday, as he faces anger over the pandemic and the ensuing economic turmoil ahead of the November presidential election.

In the polls, he is badly trailing Democratic challenger Joe Biden, who slammed the president for "walking away" as the virus ravaged the United States. Breakneck efforts to develop a vaccine or effective treatments are under way around the world, but until one is available, social distancing measures remain among the few weapons against the virus.