Trump asks 'genius' companies to help Boris

US President Donald Trump says he asked two "genius" US companies to help in the treatment of the British Prime Minister Boris Johnson, who was moved to intensive care after his virus symptoms worsened.

In a press briefing on Monday, Trump said he had asked "two of the leading companies, brilliant companies... to contact London immediately".

He did not give the names of the companies or say what treatment methods were being considered. Johnson is being treated in the ICU at St Thomas' Hospital in London.

"We've contacted all of Boris's doctors and we'll see what is going to take place," Trump said.