Greece’s stock exchange has plunged by nearly 23 percent after opening for the first time in five weeks.
It is the market’s biggest fall on record.
Immediate heavy losses were expected amid ongoing uncertainly over Greece’s economy.
Trading on the Athens bourse had been suspended since late June, amid capital controls when it looked like debt-ridden Greece could be dumped from the euro zone.
Since then, the country has agreed a framework bailout plan with international creditors in exchange for reforms and more austerity but implementation of the deal remains some way off.
Greece’s dismal economic prospects may also weigh on the market. The European Commission says the Greek economy will contract 2 to 4 percent this year, a return to the recession that plagued the country for six years until 2014.
Banking shares were particularly hard hit in Monday’s turbulent stock exchange reopening, with Greece’s top lenders down by 30 percent.