Here's why Japanese stocks have seen their worst day in five months

Asian shares were in the wars today.

The Nikkei 225 average tumbled 3.1 per cent in Tuesday trading - taking it to a one-month low and marking the biggest one-day drop in five months. The broader Topix dropped 2.3 per cent, and Asian ex-Japan shares were down 0.8 per cent.

The shift into the red is actually a delayed reaction - Japanese markets were closed for a holiday on Monday, so the slide is Tokyo's reaction to the shock US jobs report on Friday.

The yen rose sharply on the disappointing jobs numbers, as safehaven-seeking investors pushed it up, hurting exporters in the process.

Moreover, a deterioration in Japan's current account balance has made things even worse for the country's bourses. While exports suffered, the figures suggest that import costs have leapt on the weakened yen.