Fears that debt-stricken Greece may be headed for a chaotic eurozone exit loomed large as US president Barack Obama met other G8 leaders for crisis talks in Washington.

The Group of Eight top economies come together as Greece faces its second election in just six weeks, putting its eurozone future in doubt and dragging down Spain, where the government is struggling to keep its banks afloat.

European stock markets posted sharp losses, mirroring drops in Asia, while the Australian stock market closed at its lowest level for 12 months.

Facebook's shares rose less than expected on its first day of trading, despite making one of the most eagerly-awaited market debuts in history.

The Federal Government is under renewed pressure from within its own ranks to demand all Australian cattle sent to Indonesia are stunned first before they are slaughtered.