WASHINGTON - Fury has erupted over the controversial decision by the US to approve treating Covid-19 patients using the blood of coronavirus survivors.

Top scientists warned there is no proof the century-old treatment works, despite several studies offering promising results.

The Food and Drug Administration last night gave doctors emergency authorisation to use convalescent plasma, saying the 'known and potential benefits of the product outweigh the known and potential risks of the product'.

Donald Trump called it a 'very big day' at a White House briefing yesterday, adding that the approval was a 'truly historic' moment. The US President also claimed that the treatment was proven to reduce the chance of death from coronavirus by more than one third.

But scientists criticised US officials for making the 'bad conclusion' because the therapy has not been put through the most rigorous human trials, meaning there is no conclusive proof that the treatment works.

One expert, however, called it 'good news' and said he hopes the UK can soon begin to use convalescent plasma routinely.

British researchers leading a major trial into promising therapies — which found that dexamethasone can cut the risk of death in critically-ill coronavirus patients — said the move was 'ripping up good science that protects patients'.

The FDA said more than 70,000 patients had already been treated with convalescent plasma, which sees infected patients given the antibody-rich blood of survivors in an attempt to boost their immune response and fight the disease.

It comes just days after top US experts, namely Dr Anthony Fauci and Dr Francis Collins, reportedly stepped in to pause the authorisation of convalescent plasma because the evidence was not strong enough to do so.

Trump lashed out at the FDA at the weekend and accused the agency of attempting to delay the approval of Covid-19 therapeutics until after the president election in November. (FA)