By Tom Arnold and Elizabeth Howcroft

LONDON, Oct 2 (Reuters)Stocks sold off and investors quit riskier assets on Friday after U.S. President Donald Trump said he and his wife had tested positive for the coronavirus and would isolate, four weeks before U.S. elections.

Investors sought safer assets such as gold, U.S. Treasuries and the Japanese yen.

U.S. stock futures fell and European shares opened lower, although they recovered some losses in early London trading after the initial overnight move. The STOXX 600 was down 0.3% .STOXX and London’s FTSE 100 was down 0.7% .FTSE at 0930 GMT.

Shortly before 0500 GMT, Trump said on Twitter that he and his wife had been tested for coronavirus after Hope Hicks, a senior advisor who recently traveled with the president, tested positive.

He later tweeted he and the first lady had tested positive: “We will begin our quarantine and recovery process immediately,” he said.

S&P 500 futures — which fell sharply on Trump’s tweet — stabilised somewhat and were down 1.4% at 0931 GMT EScv1. Futures for the tech-heavy Nasdaq were down 2.1%% NQc1.

The MSCI world equity index, which tracks shares in 49 countries, was down 0.2% .MIWD00000PUS.

Trump’s exposure could cause a new wave of market volatility as investors braced for the presidential election in November.

How long the risk-averse moves will last depends on the extent of the infection within the White House, said Francois Savary, chief investment officer at Swiss wealth manager Prime Partners.

“We may have to wait until the end of the weekend for more clarity on the situation,” he said. “The reaction has been a bit excessive with U.S. stock futures. It doesn’t mean the U.S. administration is not able to function.”

“It will weigh on