Exports last month stumbled after four months of growth, as the upswing in the tech cycle - which had lasted far longer than expected - turned abruptly south.

Non-oil domestic exports (Nodx) fell 1.1 per cent last month over September last year, wrong footing economists, who had forecast a rise of 12.7 per cent.

This was the worst performance since December last year, and a sharp reversal from the revised 16.7 per cent export growth in August.

With the latest wave of smartphones now launched, semiconductor foundries have seen order books thin out, and Singapore's electronics boom has finally fizzled out after 10 straight months of expansion.

But while electronics exports have underwhelmed, declining by 7.9 per cent last month from a year earlier after a stellar 20.8 per cent expansion in August, shipments of non-electronics goods continued to grow.

Non-electronics exports rose by 1.9 per cent last month against growth of 15 per cent in August, partly due to the volatile pharmaceutical segment, showed data from International Enterprise Singapore.

The trade agency said that the September slump "reflected the decrease in electronics exports off the high base a year ago".

However, UOB economist Francis Tan pointed out that in September last year, electronics exports had already fallen year on year.

Economists were divided as to whether this result indicated the start of a slowdown or was a blip, although they are not changing their growth projections based on yesterday's data.

For UOB's Mr Tan, last month's export dip could be the "start of a more sustained slowdown". Even so, "we remain positive in our outlook on the overall Nodx expansion for 2017", he said.

Nomura still expects the economy to finish the year at the higher end of Singapore's official growth forecast range of 2 per cent to 3 per cent, as the economy expanded 4.6 per cent in the third quarter from a year earlier.

The Government's advance estimates already seem to assume a slowdown in September industrial production growth. "The Nodx data would appear to be in line with this," said Nomura economist Euben Paracuelles.

However, Nomura's forecast would imply fourth-quarter gross domestic product growth slowing to 1.3 per cent from a year ago.

Although Nodx to seven of Singapore's top 10 markets rose last month, a fall in shipments to Europe, Hong Kong and Thailand led the overall decline. Nodx to China, the largest market for Singapore's exports, remained in growth mode, but that engine is slowing.

Shipments to the mainland inched up just 9.6 per cent last month from a year earlier, way below the double-digit growth figures recorded in prior months. In August, Nodx to China surged 43.2 per cent.

OCBC economist Selena Ling noted that electronics shipments to seven of Singapore's top 10 markets, including China, South Korea and Hong Kong, fell last month.

Yet, this seems to be at odds with regional manufacturing indices and China's September trade data (including electronics imports), which remained resilient, she said. More data will be needed to see if the exports slowdown is the start of a trend.