The announcement of the US president’s positive test comes just over a month before the presidential elections on 3 November where he faces Democratic challenger Joe Biden.

Trump’s diagnosis has created a sense of instability in the financial markets and has led to falls in the European stock markets this morning.

The FTSE100 fell 0.6% to 5,841 with energy, mining and consumer cyclicals the worst performing parts of the market.

Germany’s DAX index traded 0.9% lower. Pre-market indicative prices suggest a 1% to 1.2% decline for the main indices in the US when its markets open later.

S&P 500 futures, which are relatively thinly traded in the early European hours, were down 1%.

Trump’s positive test also raises the question of how the US presidential election will play out – will he be well enough to continue the debating while self-isolating, and will the elections be postponed?

James Bentley, director of Financial Markets Online, says: “On a day when US jobs numbers were supposed to be the big news, markets are instead chewing over how the president’s ability to do his job will be affected by his illness.

“As Europe grapples with a surge in new infections – and introduces steadily tougher restrictions in an effort to keep a lid on them – the prospect of a power vacuum at the heart of the world’s most powerful economy has got many worried on both sides of the Atlantic. With US futures sharply down already, Friday is set to be a rocky day for the American markets.”

Susannah Streeter, senior investment and markets analyst at Hargreaves Lansdown, says: “There are already signs of a flight to safety with both the dollar and the yen rising sharply, and gold on the rise too.

“US treasuries have also jumped, as investors seek a place to hide amid what they fear could be a period of further volatility with just a month to go before the election. The virus is touching every part of US society, from the president to Amazon’s 20,000 warehouse and cashier staff in the United States who have tested positive for the virus so far.”