A sell-off in technology shares spoiled an otherwise buoyant day in the US stock market as companies from Apple to Nvidia tumbled.

Shares suffered their worst weekly loss of the year, as investors were kept on the back foot amid gathering unease around the Australian economy and after another shock poll result in the UK.

The impact of the British election for global investors comes down to one simple question.

The agency bumped up the oil giant's rating one notch, citing a strong performance despite oil price volatility and greater fiscal clarity following its $26.5 billion settlement of the deadly 2010 Gulf of Mexico spill.

The possibility of a hung parliament unnerved markets on Thursday.

• Sponsored

Three big events overnight, with the last proving to be the most dramatic, with a shock exit poll from the UK election seeding the pound tumbling. Locally, shares are due for a flat start.