Rioting on the streets of Athens and the collapse of the Greek government has sent world markets into turmoil.
Shares and oil prices plunged, with the Dow Jones Industrial Average down 180 points by midday in New York, while the price of West Texas crude had fallen by more than $2 a barrel. The hi-tech Nasdaq index was down by more than 1%.
"It's sell and ask questions later," said Steven Goldman of Weeden & Co in Greenwich, Connecticut.
Yields on two-year Greek bonds – or the interest rate the Greek government would have to pay lenders – soared to almost 28%, suggesting that investors believe the country is on the point of bankruptcy.
Fears that the contagion could spread to other European economies saw bond yields in Ireland and Portugal jump.
Larry Elliott and Heather Stewart
guardian