The Standard and Poors downgrade of the US' credit rating to AA+ is plunging markets and investors into spheres of uncertainty.

See weekly market update video below with IRG BOP's Jonathan York.

The full impact on the global economy of this move is not yet known, but the initial response is a drop in trading – with the NZX the first in line.

The NZX is at an 11 month low this morning after falling 2.9 per cent.

IRG BOP's Jonathan York explores the impact of the S&P decision on video below.