Asian and European stock markets mostly sank Friday after an outage rocked global computer systems, with sentiment also hit by US election uncertainty and Chinese economic worries.

The London Stock Exchange saw a delayed start to trading due to the glitch, which also affected airports, airlines, trains, banks, shops and even doctors' surgeries.

"Risk aversion is taking hold yet again, with news that... banks, airports, train companies, TV stations including Sky News, stock exchanges including the LSE, Microsoft's cloud services and cyber security services have all been hit by major online outages," said Kathleen Brooks, research director at XTB.

"We expect this outage to hurt the big tech companies who are also affected; Microsoft's share price is down... in pre-market trading."

Aviation officials in the United States briefly grounded all planes and airlines elsewhere cancelled or delayed flights, as systems running Microsoft Windows crashed.

Microsoft said the issue began at 1900 GMT on Thursday, affecting users of its Azure cloud platform running cybersecurity software CrowdStrike Falcon.

The tech titan said it was taking "mitigation actions" in response to service issues. 

"The world grinding to a halt because of a global IT meltdown shows the dark side to technology and that relying on computers does not always make life easier," noted Dan Coatsworth, investment analyst at stockbroker AJ Bell.

"There is chatter that cybersecurity firm Crowdstrike ran an update which didn't work on Microsoft's operating system and that caused systems to fall over. Given we do not know the full details, it's too early for investors to work out the financial or reputational impact to these businesses."

Prior to the news, investors were already on edge after a report said the White House was considering a crackdown on firms supplying chip technology to Beijing.

They were also nervous after Donald Trump's call for Taiwan to pay Washington for help defending itself against China.

Markets have been enjoying a healthy run-up as Federal Reserve officials have lined up in recent days to suggest they are ready to begin reducing rates.

However, the tech sector -- which has led the surge in stocks this year -- has taken a hefty hit after the report of the warning from the White House over supplying China and Trump's remarks about Taiwan, home to some of the world's biggest chip producers.

There is also growing uncertainty over who will run against Trump in November, as calls for President Joe Biden to step aside continue to grow owing to questions about his health.