Global stock markets dropped on Monday as the escalating protests in Hong Kong forced the closure of the financial hub's airport, adding geopolitical worries to ongoing trade war tensions.
London, Frankfurt and Paris all slid into negative territory as news of the shutdown spread, having rallied at the open.
"Hong Kong has kind of been under the radar of most traders... but increasingly I feel like that this has the potential to spiral into a bigger market worry. Today's moves highlight the risks," said Neil Wilson, chief analyst at traders Markets.com.
All flights in and out of Hong Kong were cancelled late on Monday after thousands of pro-democracy protesters flooded into the city's airport to denounce police violence.
Most of the protesters left the facility and the Airport Authority said late on Monday that it was planning to reschedule flights from 6am on Tuesday.
However, the incident turned the spotlight on the prolonged anti-extradition protests, which has left the government isolated and the police under fire.
Taking their cue from Europe, US stock markets also opened lower, "with US-China trade tensions remaining elevated, global bond yields continuing to see pressure, while the markets await a heavy week of earnings from the retail sector and a flood of key economic reports," said analysts at Charles Schwab.
"Moreover, the exacerbated unrest in Hong Kong is garnering attention and dampening sentiment as protests continued over the weekend," they said.